If Dead Heads attack low-level characters, they will lose experience and hit points. If low-level characters' hit points go below zero, they cycle to just under 65536(=2^16)
If Druids silence your party, you can still cast spells outside of combat.
There is a bug with etherealize. If you etherealize west from (0,0) you hit (15,15) but if you etherealize west from (x,0) you go to (x,15).
Enchant Item doesn't always work. Sometimes when you cast it it will reduce your spell points incorrectly. It will be off by a factor of 512 and, in fact, you will probably use fewer spell points to enchant an item to a higher level(i.e. +15 as opposed to +5).
Sarakin appears even after you defeat him.
If you rest in the Water Plane and then try to cross a boundary(i.e. go east from 15,3) you will see "can't swim."
Cast Nature's Gate from Castle Xabran, and you will wind up back in the 900's. However, if you rest or enter a town, this is adjusted.
It's possible to balloon your stats quickly. For instance, say you have an item that increases your luck. Then equip it and trade luck for personality until your luck is at zero. Un-equip and re-equip. Voila! Your luck is positive again.
If you drink from the fountain in C1 (1,11) your spell level improves to 9. As a result the computer gives knights/barbarians/ninjas/robbers the options to cast spells--although they have no spells to cast! It'd be interesting to get them to level 9 and go to Pinehurst Dungeon to get all the spells. Might be another bug...
Non-bugs, but interesting.
Lord Haart's quest is unattainable. Although you can defeat Spaz Twit, there's no other monster/item that will allow you to complete the quest.
This may not be a bug, but if you cast Town Travel(8-4) from the past, the city will be totally deserted. You can't even exit!
Recently found: behind the two fountains in A3, you hear "got me" behind the right one. Then if you go back to the fountains you can still hear the voice.