Chicken Jockeys can pass through a hole that baby zombies alone can't fit through

A baby zombie can't pass in a 1 block hole if there a carpet in front of it. (I guess it'a a half block, but i didnt test it with a slab or something else. So i dont know if it's only with the carpet)
But a Chicken Jockey is able to pass inside this hole!

It's clearly a bug since the chicken jockey must be bigger than the baby zombie alone (Or the chicken grease him up!)