I killed lots of villagers and Iron Golems in Creative mode and when i switched back to survival mode i got attacked by Iron Golems. After going far away from them and going back, they still attack. I killed ALL iron golems and spawned some new iron golems. but they still attack me.
In another world, I accidentally hit an Iron Golem in survival and I ran away. I went to another golem and it attacked me. i switched to peaceful mode but they still attack me, although i don't lose health when they attack me.

Re-create scenario:
1. spawn a superflat world (creative)
2. find a village
3. spawn iron golems(>1)
4. kill some villagers and some iron golems
5. switch to survival
6. see what happens
7. kill all iron golems
8. spawn some new iron golems
9. see what happens
10. switch to peaceful
11. see what happens