Villagers not tuning into zombies

Villagers not turning into zombies

What I expected to happen was: The villager gets killed by the zombies, turning it into a villager zombie itself.

What actually happened was: The villager died and did not turn into a zombie.

Steps to Reproduce:
1. Wait for night in a village
2. Let zombies kill villagers
3. See that not even one villager changes into a zombie