One bug that is bothering me is the bad AI Endermen have. They take blocks from the world, I'm ok with that, but this kind of 'walking loop' makes them to constantly go into water and die, making the block they had in-hand disappear.
This video shows this bug: https://www.youtube.com/watch?v=Yo35dKsFO1Y
Actually, that is the normal Enderman AI. This is not a bug.