Endermen freeze and stop moving, if you look at their face, even when they are already hostile.
They should only freeze when you're looking at their face when they're neutral and are turning hostile.
How to reproduce:
- Make sure you're in survival mode.
- Make sure the Enderman is already hostile towards you.
- Place your crosshair at the Enderman's head.
- --> The Enderman freezes in place
(So in short, for neutral endermen this works as it should, but not for hostile endermen.)