Zombies stop attacking villagers that are frozen in place

I'm doing a build with villagers that are frozen in place and zombies can come attack them.

What I expected to happen was...:
The Zombie should've gone up to the villager and hit it until it was dead.

What actually happened was...:
The Zombie attacked the villager once, then just stood there and did nothing.

Steps to Reproduce:
1. Set up repeating command block: "/entitydata @e[type=Villager] {Motion:[0.0,0.0,0.0]}
2. Spawn a villager
3. Spawn a zombie to attack the villager