Edit: people are right it seems like I didn't wait long enough. The code is there and no reason for that to not work.

Zombie Villagers are supposed to become normal villagers when they are affected by weakness and given a golden apple ( a feature added in a snapshot). But currently when you give the zombie villager the apple, it only changes the potion effect on the zombie villager (with a sound effect), but doesnt restore him back to human.