i found that if you log out in multiplayer while riding an horse, that horse will be duped when you log in.
MC-16020
duplicating horses
Resolved
Duplicate
0
jai jhurry
(Unassigned)
Unconfirmed
horse
Snapshot 13w19a
Retrieved
31st Duplicate of MC-13737, please use the search function to see if your bug has already been submitted. Currently over 56% of tickets are being closed as duplicate.