May be a deliberate thing or already reported but i was in the nether and whilst swinging my sword at a wither skeleton a zombie pigman walked right in the way, this of course (as expected) angered it and all the others in the area. After running to the safety of the overworld and continuing to work on various bits and pieces i decided to go back to the nether, i thought the pigmen would have calmed down... No, they came running at me, ok not an issue, run a hundred blocks or so away so they despawn... Found the pigmen over there were angry with me too! Run back to the overworld, play some more, log off the server and go to bed. Wake up in the morning, return to nether and get rushed by pigman, not an issue, in preperation for this i left everything in overworld... allow it to kill me, return to nether and get killed again...