OS: Windows 7 (ver 6.1, arch amd64)
Java: 1.7.0_13 (by Oracle Corporation)
Launcher: 0.8.1 (Dev) (bootstrap 2)
When you open a chested horse inventory obtained through a 3rd party tool or through the /summon command, it crashes the game.
Dinnerbone on 24/May/13 11:16 AM :
Horses are not supposed to have chests.