Iron golems collide with walls

Iron Golems can't detect walls correctly, so they collide with them. Their movements are slow, so they keep colliding for more time than normal mobs.

This is annoying. OK, they are golems, don't have brains... But they have eyes! They need to see things in their way and detour.

Video: http://www.youtube.com/watch?v=j3SlHmjtA8A