Here are a few more weird or amusing bugs that I have had to fix in Din's Curse because of the crazy amount of possibilities that exists in the game.
We had another amusing summoned monster issue that I fixed. When you hurt a monster it tells your minions that they should attack that monster also. Well when you cast something like a fireball, it also tends to do damage to objects like lifestones that you usually don't really want to destroy. However, your minions don't know that, they just know that you attacked it and they should too.
We used to have a bug where zombies and skeletons that were buried could roam around underground. In DoP we have a monster that really can do that but zombies and skeletons aren't that good at digging.
Monsters tend to get a little pissy when something damages them. Unfortunately sometimes they aren't very smart about it. At one point in time monsters would try to retaliate against ground traps that can't be destroyed. What's worse is they were very persistent.
DC allows you to get a little creative in how you kill things. For example, if there is a monster standing near some poison barrels, you could destroy the barrels and the monster will likely die from the poison. Unfortunately, you didn't use to get the credit for the kill.
Here's another weird side effect. Sometimes you can get a quest to go kill some Scarabus' that are causing problems. Well actually killing Scarabus are pretty difficult since they are basically suicide bombers. Now days you just have to be the last one to hurt it to get credit if they explode.
Undead pretty much attack anything. I actually have to go in and tell them what they aren't allowed to kill on sight, things like cave-ins and recon totems.
Tornado and ice storm spells at one point in time put fire elementals out just like a normal fire. It was kind of cool but a level 1 tornado would destroy the highest level fire elemental boss in 1 shot.
The thief specialty has a disarm skill and pools of oil, alcohol, and other similar things are considered traps by the engine. You see where I'm going right? A thief would walk over a pool of oil, disarm it, and it would disappear. I guess we should send a thief out to the gulf.
At one point in time cave-ins showed up on the mini-map like monsters as red dots. This wasn't too big of a deal until there was a huge cave in somewhere and you bothered to look at the mini-map and noticed what looked like an invading army.
At one point in time Din himself could get poisoned or petrified. This reminds me of a bug in Ultima Online where someone managed to kill Lord British.