Pandas are often buggy.  They freeze, get stuck in animations, and often don't respond to bamboo.  One panda was hostile for very a long time after hitting him.

• I found a panda and fenced him off in an enclosure.  (I put a name tag on him)
• At one point, the panda became frozen and had no animations, he would not respond to anything, and wasn't moving.
• I hit the panda to try and see if it would get un-frozen.  The panda did un-freeze, but, now he has abnormally long-lasting hostility towards me.

This didn't just occur with one panda, it is happening to all pandas across my world.  It seems like they are generally buggy or might have some kind of lag.