If you have a Villager get attacked by a Baby Zombie in Hard mode, it could rarely turn into a Baby Zombie Villager.
To Reproduce:
Step 1: Spawn or find a Villager
Step 2: Spawn a Baby Zombie near the Villager
Step 3: Have it turn into a Zombie
NOTICE: This rarely happens, so you have keep trying to do it
Linked issues
is duplicated by 6
MC-64406
Chicken Jockey spawns when villager died
Resolved
MC-67096
adult villiagers become baby zombie villager
Resolved
MC-75712
Villager turns into Baby Zombie Villager
Resolved
MC-87256
Zombie villagers
Resolved
MC-87307
Villagers can turn into baby zombie villagers when killed
Resolved
Comments 7
I've seen this somewhere around four times. When a villager is infected by a zombie it has a very small chance to turn into a baby zombie villager instead of a normal one. Doesn't make sense, but it's due to how zombies naturally spawn. I don't know if this happens in the latest snapshot, it probably does though...
Doesn't make sense as intended, so it seems more of a Won't/Can't Fix (based on above comment). (Affects 1.8)
Also MC-64406 is related/duplicate.
I also noticed that they can spawn with weapons, and normal villagers can spawn as baby zombie villagers.. I'm guessing this will be hard to fix. The game senses when a villager is killed by a zombie. It then spawns a zombie with the "IsVillager:1" tag. This means that adult villagers have a 5% chance to create baby zombie villagers. When a baby zombie/baby zombie villager is spawned, it has a 5% chance to spawn as a chicken jockey. This means that even regular villagers can be baby zombie villager chicken jockeys. This is just a guess, but it provides a reasonable explanation to this bug. The idea of a "can't fix" seems like the best resolution. You could technically fix this, but it would be more trouble to fix than it causes.
EDIT: If my guess is true, then this means that a baby villager killed by a zombie will have the "IsVillager:1" and "IsBaby:1" tag.
Probably a bug in these snapshots that Mojang made.