I had spawned in a donkey using a horse spawn egg because I was tired of looking for horses on my snapshot server.
I had it tied to a fence post with another horse with leads, and I right clicked on it with a chest in my hand, and my game crashed.
Environment
OS: Windows 7 (ver 6.1, arch amd64)
Java: 1.6.0_27 (by Sun Microsystems Inc.)
Launcher: 0.8.1 (Dev) (bootstrap 2)
Duplicate of MC-16148, please use the search function to see if your bug has already been submitted. Currently over 56% of tickets are being closed as duplicate.