This happens with most mobs. Confirmed ones are Creepers, Wither Skeletons, Skeletons and Zombies.

Whenever I hit a mob for the first time in combat, they start to move very slowly and shaky, almost as if they hesitate to come nearer, which makes it really easy to hit them again.

I don't know if this is part of the new AI, or just a bug, but it seemed more like a bug to me, as it makes no sense for melee mobs to hesitate about attacking; it just turns them into an easier prey.

Usually one out of two mobs show this behavior, so it's pretty easy to reproduce.