Problem with mob AI-only effects some mobs

Put the summary of the bug you're having here

What I expected to happen was...:
After encountering a hostile mob (zombie/skeleton) in survival mode, I expected to be attacked regardless of whether the mob was being hit with arrows

What actually happened was...:
when a zombie/skeleton was attacking me, and was then shot with an arrow (from the player or another skeleton), it would stop for a moment, seemingly forgetting me, before continuing to attack.

Steps to Reproduce:
1. Find/spawn/summon a skeleton or zombie (I tested, does not work with other mobs)
2. Make sure you are in survival mode and that the monster is attacking you
3. Shoot the mob or get a skeleton to shoot it
4. See what happens!