I was able to recreate the bug. Do NOT try this on your precious worlds. I can't log on the worlds I tried this on, it keeps on crashing.
1. Place a rail down.
2. Place a Barrier Block on top of the rail.
3. Place the Minecart on the rail.
4. Right click the cart.
Crash Pastebin: http://pastebin.com/MBQKPxUn
Had this happen to me too, was able to re-enter the world by opening with previous snapshot.