When Baby Zombie wears a Mobhead the mobhead floats at normal Zombie height. I know this used to be a bug for baby zombies wearing armor and they fixed it (I can confirm that armor works with them now). But they didn't include mobheads in the fix. Also you might want to check if wearing pumpkins or jack o lanterns has the same problem.
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CubeTheThird
Duplicate of MC-2664 - If you have not , please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
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Sorry for not spotting that. You're absolutely right it is a duplicate. I knew the general armor bug had been reported (and since fixed) but I didn't realize the seperate "mobheads still broken" bug had been reported.
CubeTheThird
No worries.