In a Multilayer game when you ride a horse and log off and log in you would still be riding the hose but it would spawn a new horse.

How to do:
Get 13w17a
Start a Sever Lan Or The other one
Get a horse
Make Friends With The Horse
Get on horse using a saddle
Log off and log back in to the Server
Now you have two horses.

Ps.
I have a video of me doing it if you want to see it.