Note: I haven't tested this with baby zombie villagers on normal villagers.
When a head is put on top of a zombie villager, it is displayed slightly too high. I have retextured it's normal zombie villager head invisible, and put a default player's head on it, the screenshot below shows the gap between the neck and the head.
I'm working on an adventure map, and if this is fixed it would be appreciated 😃
Is this still an issue in the current Minecraft Snapshot 15w47c or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
If so, please provide the exact command you're using.