If a pigman is damaged by another mob, then you later kill that mob, the pigmen around the damaged pigman swarm you as if you attacked him. I’ve found inconsistencies with the mojang report that I posted below. For example, if you run, without retaliating on any of the aggro’d pigmen, they’ll forgive you in the normal amount of time. Also, I did find that the “aggro radius” was larger than normal, but not 500 blocks.
I thought I should warn people about this, because it can be a pretty nasty surprise if you’re not prepared for it, and it makes wither skeleton farms virtually unusable.
See the official Mojang bug report: https://bugs.mojang.com/browse/MC-69032
Some video evidence from the report:
https://www.youtube.com/watch?v=vokGKpkYV_Q
https://www.youtube.com/watch?v=6AkJd8EOpeY
Sorry if this is old news. I haven’t played 1.8 until recently and a couple days ago was my first real nether visit.