I have a system where a villager is put through a machine and made into a zombie villager and then while sat in a mine cart I turn them back into a villager

What I expected to happen was...:
the villager to be sat in the mine cart like normal.

What actually happened was...:
the villager sinks into the ground on completion of the transition and will sit normally when the mine cart is moved

Steps to Reproduce:
1. put villager in mine cart 
2. get zombie to turn him into a zombie villager
3. watch