Closing Fence on Mob CRASHES Game

I closed a fence on a cow (like I always do) to try to stop them from coming out and the game crashed.

Attached the crash report it gave me. It says server not client. Forgive me I don't know what that means but I was in single player not hosting a LAN or any other type of server. Also I had a lot of cows and sheep and it lagged my game every time I looked in that direction. But this is the only time it crashed. I am in 1.9.1 pre 1 right now. I was in Official 1.9 before this. Same world, of course I backed it up before i use another snapshot.

I couldn't find anything about fences crashing the game so I made this ticket.

UPDATE: I just tried to duplicate this in 1.9.1 pre 2 and I was closing the fence while the cow was standing in the fence gate and it didn't happen. So either it was fixed in this version or what happened was some sort of fluke. I have no idea. But it took a few attempts to do this so that could be the case.. At present I am attempting to make this happen again in the pre 1 version and I have succeeded. However this time I opened the fence gate while the cow was trying to get out. I will attach the crash report it gave me.

1.9.1 pre 1 - first one 3-10-10
1.9.1 pre 1 - second time 3-10-11

UPDATE 2: I made a new world in 1.9.1 pre 1 Flat world. This doesn't happen at all. I am stumped. Also I went back to the world that this first happened and attempted it again, this time the crashes happened when I just opening/closing the fence gate while walking. It only happened occasionally though. ALL of the crashes, I had something in the left hand slot nothing in my right hand. But it doesn't seem to affect any of my other worlds for some reason. Maybe it just my world?