When I set render distance to 32 chunks, then all mobs freeze.
It is impossible to hit them, they do not move, make sounds or anything. The player seems to be unaffected (except he cannot drop items, nor do items drop from broken blocks).
When the render distance is lowered, the problem persists. After quitting and entering the world again, it is fixed.
I can confirm this too. I've seen it in the nether.