Still happening in 1.5.1 – Added screen shot.
I'm also very chatty from time to time so I probably type responses and chat with multiple players more than your average bear.
Vanilla. I like to run the latest version right when it comes out! 😉 No time to wait for Bukkit!
It doesn't matter what type of farm mob it is.
I've got sheep, cows, chiduckens and pigs all in separate pens (wooden fence.) One mob of each is stuck in the NW corner and only the NW corner. If you attempt to lure or breed with respective food--they cannot be lured and the other mob must come to them for the breeding to work. If you punch or attack the mob with a tool or weapon, it will not move or run.
That is correct. (I apologize for the late response.)