Bugs

All currently known bugs in the Ultima series are listed here. Note that bugs that can be exploited for cheating are not listed here. Also note that some descriptions of bugs necessarily contain spoilers for the games.

Akalabeth

 * In the Black & White DOS version distributed on GOG, Lord British will not recognize any quest progress.
 * The Apple version will falter if you first visit Lord British with a Wisdom of 33 or higher, dropping the player back to the "lucky number" screen. This is possible by becoming a Lizard Man with the amulet.

Ultima I

 * When you rescue a princess in some castles, she can get you backed into a corner forcing you to kill her to get free (yeah, some rescue!).
 * Dungeon levels don't stay the same in the original (non-remake) Apple II version. Thus when the player climbs down and then back up again, the layout will have changed, so that maps will be useless. While this might be considered a feature rather than a bug, it is not there in Akalabeth and thus probably is a bug.
 * The original (non-remake) Apple II version uses an undocumented 6502 opcode that makes it impossible to hit the alien ships to become a Space Ace when using a 65C02. (The fix is in file "FGT3". Change the bytes at 74D1 to 46 43 45 43.)
 * In the PC version, the player's armour seems to be of no effect when fighting occurs in a dungeon. This makes the dungeon quests much harder than in the non-PC versions of the game.

Ultima II

 * In all versions, the numbers for attributes and hitpoints can "roll over", meaning that they return to zero when the value would go over 99, or over 9999, depending on which statistic it is. In order to avoid reaching this situation in case of hit points (having zero hit points will kill the player), Richard Garriott made Lord British ask for more gold for hitpoints the higher the character is, so that the danger of rolling over is lower. Also, prices roll over when the sum of Intellect and Charisma reaches 160. The Ultima II Upgrade Patch fixes this for the PC version, but actually it is sufficient to stop grinding when the attribute gets near the "roll over" value.
 * In the original Apple II version, it's impossible to increase the "strength" attribute in-game. A patch for this exists and can be found in the usual Apple emulation archives.
 * The PC version of Ultima II isn't made for fast computers and crashes with a "Divide by Zero" error. Thankfully, the patch mentioned above fixes this as well.
 * The latest variants of the PC version of Ultima II, that came in CD compilations such as Ultima I-VI Series and Ultima Collection, got broken. The game originally came on three floppies, during a time when MS-DOS didn't yet have sub-directories. Some files on the second floppy had the same names as some on the third floppy, but their contents were different. When it was all put into one directory for the compilations, the person(s) who did this seemingly didn't realize the file contents were different even though the file names were the same, so that some of the planet maps from the third disk got overwritten. While this didn't make the game unwinnable (the one planet, other than Earth, that absolutely has to be visited by the player was not affected), it certainly reduced the game's enjoyment and caused considerable oddness (most planets now looked exactly like the different eras of Earth, minus the time doors). The patch mentioned above fixes this as well.

Ultima IV

 * The are several bugs in the conversation structure data, making certain conversations impossible to reach. There are also a few misspellings in the conversation key words, which prevent the player from getting the right answers unless he also misspells the key word in exactly the right way (highly unlikely unless the player looked at the code). For example one character expects to be asked about reasearch instead of research.
 * Especially the Apple II version has a large number of misspellings in the conversations. In the later ports, some of the more obvious ones were fixed, but others remain.
 * In the Apple II version, Shamino and three other persons surround the talking Ankh of Spirituality from all four sides. This prevents the player from getting access to the Ankh unless he first asks Shamino to join him on his quest. In case the player himself is a Ranger however, Shamino will refuse to join, meaning that the only way to talk to the Ankh is by first un-virtuously attacking one of the four peaceful persons that surround it, and then either un-virtuously killing the person or un-virtuously running away. In later ports, Shamino was moved one square to the west, so that the player can stand between him and the Ankh and thus talk to the Ankh without trouble.
 * The correct way to exit the balloon is to land it first, then exit it. The Apple version, however, had a bug that allowed you to exit the balloon while it was still in flight. This put the party into a confused mode. This mode was mostly like that of being on the surface, with the notable exception of non-occlusion, and inhabitants and monsters behaved as though the party was in flight.
 * In the Apple II version, if the player character already has 9999 experience points, they must not lose the eighth of Valor. This is because the game stops giving the player valor points when the experience maximum is reached, making the game unwinnable should the eighth of Valor be lost at that point. This was fixed in at least the C64 version.
 * In all versions for MOS-6502-based computers (Apple II, Commodore 64, Atari 8-bit), there is a bug that prevents two thirds of the shrine messages from ever appearing. Apart from the special message that a player gets when achieving partial enlightenment, each shrine is supposed to have three different things to say, depending on the number of meditation cycles chosen by the player. However, the player always gets the same message from any one shrine in these versions of the game. Fixes for the Apple II and the C64 versions exist and are floating around in the usual emulation archives.
 * At least in the DOS, Apple IIe, C64, and FM Towns versions, dungeon Hythloth is bugged, as two rooms in level 6 are broken, lacking a trigger for the exit wall in the eastern room, and incorrect start positions in the western room. Fenyx4 fixed this with a patch, found here.

Ultima V

 * The game has a bug on the PC version that is more of an annoyance. When starting the game with NumLock still activated on the keyboard, the normal numeric keys, apart from 5, won't work due to mapping confusion, making finding the Sandalwood Box and camping for raising levels impossible. Thankfully, the easy solution is to turn it off before starting the game (or DosBox). Modern computers have it turned off as a standard.
 * The Atari ST version of the game has a critical bug later in the game. The bug happens completely at random and will manifest in the game suddenly asking for the game disk that actually is already in the disk drive. The game will hang immediately afterwards, forcing a complete reset of the computer.
 * The Amiga version of Ultima V is very bad at reading the keyboard. Too often, keypresses will either not be read at all, or will "stutter" and (for example) a single keystroke will be interpreted as three. This makes playing the game very tedious at times or result in unwanted, bad situations.

Ultima VI

 * If a companion dies and the party then is filled to the maximum of eight, resurrecting the character will turn the companion in question into a zombie that follows the player. Since the party can only have eight characters, the 9th member screws up the game until it crashes.
 * The C64 version has an annoying bug (at least on emulators). When talking to Xiao, trying to buy spells from her results in her telling a part of dialogue from Isabella. This bug is only plaguing certain versions of Ultima VI on the C64 due to a faulty image of the populace disks that is wide-spread, and the only way to go around the problem is to use the internal cheat system to get the spells Xiao would normally sell the Avatar. A fixed version does exist, called "Htw-fixed".
 * A very bizarre bug in the C64 port, at least in emulation, causes the game to display "Aaaaaaaaaaaaaaaa" whenever the action of looking at a person should show the name and when talking above the dialogue of the NPC, where the name should have been as well. The dialogue itself is not affected.
 * The Amiga version of the game has a bug that after some hours of gameplay duplicates the inventory of the party during a loading or saving of a game. All the items are permanent and the bug will repeat itself, meaning that it will slow down the game considerably.

Savage Empire

 * A bug sometimes happen in the sequence where the Avatar has to kill a Tyrannosaurus with a boulder. If the bug happens, a random party member will be frozen forever.
 * Another bug may happen after uniting the tribes. Leaving the Myrmidex caves after having beaten the Great Drum results in the player being stuck in an infinite, self-repeating grassland.
 * Items that are left in a location, such as a village hut, can disappear. Note this is particularly important for quest-related items. Confirmed disappearing items include the fire extinguisher, bucket, and jugs of platcha, as well as easily replaceable items like sabretooth tiger skins, bamboo flintlock rifles, and bows and arrows. While it is unclear whether this is caused by a proper bug or quick-fingered natives, in order to avoid restarting to complete quests it's a good idea to keep all unique items with the party.

Martian Dreams

 * The game can freeze when saving, and the saved file gets corrupted. A savegame seems to reliably corrupt itself if one saves in the area north of 31°15'S and east of 158°00'E unless one had previously saved in the area south of 31°00'S and east of 158°00'E at least once some time before that. A simple solution is to save near Dibbs before going north.

Ultima Underworld

 * There is a bad bug that allows the character Judy to sometimes walk into lava and die, thus making the game unwinnable.
 * The floppy disk version of the game had a bug in the lower levels, known as the "inventory bug". It would strike at random when changing levels, screwing up the inventory which generally resulted in loss of vital items. The CD-version fixes this bug, but it re-appeared in the PSX port. A detailled reason follows, as the cause is the game engine. The reason for this bug is the way the game manages items in the world. There is a hard upper limit for items on a level, which is calculated by adding together the player's inventory, actual items on the level and "decorative" items like bloodstains. Fighting a lot on a level (creating bloodstains) and dumping items a lot in it could result in reaching the limit. Entering the level next time, items are deleted from the inventory in order to get under the limit again. The patch did raise the item limit per level significantly, thus making it very hard to encounter the bug. The sequel fixes this by deleting decorative items (like bloodstains and bones) once things are near the limit, which is raised as well.

Ultima VII

 * In certain circumstances, a red frame appears around the screen after you have enlightened a torch. Alas, it does not disappear.
 * A bug in the floppy disk version of the game was that keys tended to simply disappear, making the game unwinnable. Origin fixed this problem in the CD-version.
 * Another bug makes even the walls of the houses disappear. This bug is not limited strictly to walls; carrying too many items, or having too many items on screen at once, will cause various objects to 'vanish' as the game runs short of memory.
 * Things that once stowed in your inventory do not always come back.
 * Flying with the Magic Carpet to Minoc has the effect of the murder site being cleaned up immediately. This makes the Serpentine Dagger vanish, thus it becomes impossible to confront De Snel. The only workaround is using another Serpentine Dagger, since another bug is that they are all the same.
 * Another bug with the carpet appears when flying over the Isle of the Avatar. Unlike other sliding doors, one in the dungeon below that island closes even if flying over the mountains under which it is. This makes the final dungeon un-winnable.
 * Due to a bug, it is impossible to get Rankin to talk the truth with the cube. This was fixed with an Exult mod.
 * Trying to read the Golem-ritual scroll after having left the Test of Love results in a crash.
 * A bug in the German version: some conversation topics do nothing when clicked on, as their triggers are missing. This was fixed in Ultima VII auf Deutsch.
 * It is possible to kill Cador in a bar fight, and then tell Yvella about where Catherine goes at noon. This creates the interesting situation where Cador lynches Lap-Lem despite already being dead.
 * If the player's name is "Avatar", it becomes impossible to ask Tseramed into the party. The conversation tree gets stuck in a loop where the player cannot answer with his true name, leaving the only options as "fellowship" and "Avatar". Choosing "fellowship" will end up with a dialog tree that has only the choice of "Abraham" for the character's name. Identifying oneself as Abraham will make Tseramed either attack you or send you on your way, depending on subsequent answers. Choosing "Avatar" acts as if the player has said they are The Avatar, not that their name is "Avatar". This makes it impossible to get the join option for Tseramed, since it will not appear until the player has given him their name. Eventually the dialog tree can get into a state where there are no options available and the game is frozen. It appears that hex editing the occurrences of "Avatar" in the save game file to another word fixes the issue.
 * When wasting a potion (like dumping its contents on the floor), a party member scolds you. However, instead of the proper "mylord" or "mylady", the party member says "(Gender)". The usual gender-call in the dialogue code was misspelled, causing the placeholder to appear instead.
 * The dialogue structure of the Iskander-quest is bugged, meaning that the quest can't be solved.
 * Fishes were accidentially given a size of 0, thus making it impossible to go fishing. This was fixed in Exult.
 * Another bug of the German version. Due to some accidentially removed piece of code, single reagents found in the world register as quantity 0, this don't add to the reagent pool and vanish when added to a stack. Also fixed by Ultima VII auf Deutsch.

Ultima Underworld II

 * Being nasty to Nanna results in a bug that creates a never-ending servant strike, essentially becoming a plot-stopper since events in the game proceed with plot development. This was fixed in the CD-version.
 * Getting the Horn of Praecor Loth by destroying Praecor Loth results in a bug where the endgame (the appearance of Mors Gotha in the castle) can't be triggered.
 * There is another bug which can cause the endgame to not trigger. The Djinn Bottle has to be placed in the center of the pentagram before breaking it. While it seems to work when putting the bottle near the edge, it actually doesn't. This can be fixed by getting the replacement bottle from the Void and doing it correctly.
 * The game would crash from a “divide by zero” error if the player attempted to jump over a Fire Elemental.

Serpent Isle

 * All of the ghosts in the game (such as the ones in the Exploded Powder Mill) are the Chaos Hierophant. Talking to him before the right time will result in plot-stoppers.
 * Also, the pillars in Isstanar's room teleport accidentally to the test of purity, resulting in plot-stoppers.
 * One bug in Monitor can make the pikeman at the List Field, who manages the training, disappear. This bug lies in the banquet scene, and is related to the handling of internal game eggs (triggers). The usecode deletes the nearest egg trigger to the Avatar when opening the door to enter the banquet, which can erroneously be the Pikeman spawn egg for the List Field if you are to the west of the Banquet Hall. To avoid this, approach the banquet from the east.
 * One plot-stopper bug prevents Xenka from speaking about "sacrifice". The cause is the usecode egg in the small chamber in Furnace where the Serpent Staff is found; this egg sets a game flag which influences Xenka. The Exult team has a good forum topic on this bug.

Ultima VIII

 * Beren's dialogue, when reaching the lava river after cooling it partly off, is buggy. Most of his lines vanish. The cause is flag problems. This can be avoided by either never talking to him, or angering him in Tenebrae and denying an apology.
 * It is possible to speak from the fourth Ancient Necromancer onwards without the use of Death Speak.
 * A rather nasty bug is that, after getting the Breath of Air, the Avatar can use it right away on the present Stratos, regardless of game progress, and gets transported into the Ethereal Void afterwards, bringing the game to a dead end, since it now isn't possible to progress any further (unless the Avatar has the other blackrock pieces already).

Ultima IX
The game has so many bugs and plotstoppers, it's impossible to list them all here. A short overview of the effects involves complete breakdowns of the game, plotstopper and other flag problems, graphics corruption, a never fixed memory leak that forces a restart after a certain playing time and countless weaknesses in the AI of characters and enemies.

Weaknesses in the Ultima IX Physics describes how these bugs affect the physics engine.