My Zombie Pet Changed Into A Horse???

Hey everybody, I bought a zombie pet (back before 1.12 when the eula crushed our hopes and dreams). It has always been a humanoid standing zombie, when I logged on today i gasped for my dead companion had become a horse and this is not normal you see. Can someone please explain whats happening, this is making me very sad considering I paid 20 dollars for it when it came out and i already have the zombie horse skin for my actual horse.....

 

Lol its thanprob your horse

 

that moment when im on an account i just made that has no horse :O

 

i like pie

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i rly do like pie