This bug has to do with the bulette, found in the Underdark. There are a few things I've noticed:
1. The ground will shake and knock down all my characters, but I cannot get out of the situation with out saving and relogging. Sometimes the Bulette does not even show.
2. After fighting a bulette, the creature's label/health bar will not leave the screen, even after going back and forth from camp.
3. I assume this is on purpose, but I have yet to kill one. They disappear shortly after receiving just a little damage.