Ahdarji's Heirloom glitch
There are several major glitches during Ahdarji's Heirloom. One of the more significant is triggered if you have previously completed Sanguine's daedric quest. See here for more details and possible fixes.
Horse Mounts Glitch
In all versions of Oblivion and Shivering Isles, mounting a horse while your character is seated will cause strange graphical glitches and freeze the game. More information is available here.
Lost Quest Items
Most items that are critical for completing quests are tagged as quest items and therefore remain permanently in your inventory: you cannot drop them, put them in a chest, or sell them. However, there are a couple of known ways to lose such items.
- If you go to jail and break out, quest items will not be found in the Evidence Chest. You can recover any quest items by going to jail again and serving your sentence.
- Falcar's Black Soul Gems for the Cheydinhal Recommendation quest can be used as regular Grand Soul Gems. If filled with a soul, they can be used to create an enchanted item or recharge a weapon, at which point they will disappear.
See here for more details on this bug.
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This bug is fixed by the Unofficial Oblivion Patch.
Unexpected Voyage Crash
The game will crash if you start An Unexpected Voyage while The Elven Maiden is also active.
See here for details.
- This bug is fixed by the Unofficial Oblivion Patch.
The Ultimate Heist
After pulling off the Ultimate Heist, it is possible to become permanently stuck in "cutscene mode" after watching the conversation between the Countess of Anvil and the Gray Fox if you have the wrong Thieves Guild rank when you do this quest.
You will end up with the wrong guild rank if you complete any other Thieves Guild advancement quests between obtaining the Arrow of Extrication and the end of the Ultimate Heist. This is only possible if you trigger a glitch that allows you to do the Thieves Guild quests out of order, in particular by exploring the Temple of The Ancestor Moths prior to starting Turning a Blind Eye.
See here for details.
- This bug is fixed by the Unofficial Oblivion Patch.
Empty Spell List Crash
On the PC, if you use the keyboard (Up, Down, Enter) to buy the last remaining spell in a spell vendor's list, the game will crash. Regular vendors will not trigger the glitch, nor will buying the spell with your mouse.