Put the summary of the bug you're having here
When in a fortress in the nether hunting Wither skeletons, blazes often spawn. If the blaze's fireballs happen to hit a zombie pigman when I am in the the are, the pigman will aggro and attack me. It will cause all other pigmen in the area to aggro as well.

What I expected to happen was...:
I would expect the fireball to damage the zombie pigman without causing them to aggro towards the player.

What actually happened was...:
When fireballs hit pigmen, they aggro and attack the player.

Steps to Reproduce:
1. Go in a nether fortress, look for either a blaze spawner or random blaze.
2. ...Intice the blaze to shoot fireballs, hopefully angling yourself between a blaze and a pigman.
3. ...If the fireball hits the pigman, be prepared to run for your life.