The Hitbox on a Zombie Villager isn't the same as a regular Villager! One of my Villagers got converted and then suffocated in a block after it's hitbox was raised ever so slightly due to becoming a Zombie Villager. (I have a snow layer base) I'm no Zombie expert; but I'm pretty sure being infected doesn't help you grow!

If the hit box was shrinked to be the /same/ height as a regular Villager (Like it should) this irregularity would be eradicated as well as that we'd have a sure-fire way of organising Zombie Villagers from regular Zombies! So there is a positive to it to! I'm sure its not too hard to fix! Sure, it's a bit petty. But, i think it's worth adjusting to avoid losing villagers to suffocation!