Iron Golems not attacking zombies

Iron golems were near zombies in a village and they did not attack them. This has occurred in Creative Mode and the golems were created, not naturally spawned.

*What I expected to happen was when iron golems saw the zombies, the zombies would be attacked by the golems.

*What actually happened was the iron golems walked around as if there were no hostile mobs to attack

Steps to Reproduce:
1. Create a new world
2. Wait until night time
3. Create an iron golem
4. Wait for a zombie to spawn or spawn one yourself near the golem