Zombie Pigman becomes very slow (like laggy) when aggressive while FPS stays the same

Zombie pigmen move ridiculously slow when aggravated they're causing lag where in there is a delay when opening chests etc etc.but my FPS is still ok

So I built snocrash's gold farm a few snapshots ago, and it still works fine, I jumped to 16w02b and used the farm, when I hit a pigman they pathfind to me but they're very slow and the chests are also delayed when opening and closing, but my FPS is maintained at 100-200FPS approx*

go to the top of the nether and build a platform at y 240 and hit a zombie pigman to get them aggravated