horses corrupt player data

Put the summary of the bug you're having here

You can ride horses with some friends

that you can have a fun battle on horses

you would sit on a horse and it would kick you from the server and would not allow you re log in my friends mac would do the same

Steps to Reproduce:
1. make a multiplayer server
2.make a horse
3. get to the point where you can sit on it
4. sit on the horse