Zombie pigmen do not seem to be losing agro. I have gone outside their follow radius, waited 2 minutes, went back, and they immediately agroed to me. I have done this multiple times. Every time the pigmen are still agroed when I come back into their follow radius.

Also, in the past one hit kills did not cause additional pigmen to agro, but this is no longer the case. I don't know if this is intended, but it makes pigmen nearly impossible to escape, in addition to the  issue mentioned above.