iron golems act like hulks

What I expected to happen was...:
that the iron golem just acted normal

What actually happened was...:
the iron golem uses his arms as fast as a machine gun and beat mobs to death in less then a second

Steps to Reproduce:
1. create an iron golem
2. spawn a hostile mob in a corner/near a wall
3. the mob doesn't get threw away (if he is stuck in a corner, wall or other block that prevent him from getting knockback)
4. the iron golems rapid fires him to death O.o