ToME: the Tales of Maj'Eyal

The Stone Warden's Elemental Split talent causes the Exterminator Quest in the Infinite Dungeon to stop working. When the summons despawn the quest description ceases to list the remaining enemies and the quest itself will remain perpetually unfinished when you leave the floor, never either succeeding or failing.

Yes, any kinda clones will break the quests (Exterminator becomes impossible to complete, most others automatically complete successfully when the clone expires)