Basically most, if not all mobs dont turn themselves properly to face the player. Instead of moving entirely to face the player, mobs turn themselves in small portions towards the player.

To reproduce:

1. Spawn or go to a mob, like a Chicken, or a Rabbit.
2. Wait until they start looking at you.
3. Move slightly to the side. They should move themselves properly to continue facing towards you.
4.  Now move behind the mob so they have to turn their body around to face you.

What should happen on step 4 is the mob should just spin around to face you smoothly, like how its suppose to be.

What really happens is the mob will try to face you, but will spin around in portions.

Also this is a video showing the bug, because the file itself was too large to put here on the tracker: https://youtu.be/la7IUv9rMyw