Hi,
If you put a horse in fence square to keep it inside and try to move it without hit it (by moving to it and trying to move by collition) it will escape.
I only seen it in the small horses.
Environment
MacBook Pro
Procesador 2,9 GHz Intel Core i7
Memoria 8 GB 1600 MHz DDR3
Gráficos Intel HD Graphics 4000 512 MB
Software OS X 10.8.3 (12D78)
Duplicate of MC-13632.