villagers not turning into zombie villagers but die instead

Put the summary of the bug you're having here

What I expected to happen was...:

so I was going to infect a villager and turn him into a zombie villager then

What actually happened was...:

the zombie kill him and the villager didn't turn into a zombie villager 

Steps to Reproduce:
1. put the villager (doesn't matter if he has ANY trades or not) in a minecart 
2. put the minecart with a villager in it next to a zombie doesn't matter what hes got or if he has a nametag 
3. then the villager dies in stead of turning into a zombie