I searched and found nothing on this specific issue, unfortunately.

Somehow, my parrot, Pete, got himself stuck in my donkey, Lazy River. I can no long ride Lazy because Pete has hitched a permanent ride. I can take Lazy's saddle off and I can open the chest attached to Lazy, but Lazy cannot be ridden and does not move or make noise.

So, I figured I would just spawn a new parrot and kill Pete through cheats. I did, and the game told me Pete had been killed, but Pete is still there and Lazy still won't move, even when pushed, nor can I ride the donkey. I continue to enter the cheat, and it continues to kill Pete, who continues to sit inside Lazy.

Animals can walk straight through Lazy without a problem like as if the donkey isn't even there. I can still hit and feed Lazy. FYI: there are two+ blocks of space above Pete, so he has the room to move off of Lazy.

I also cannot control Pete, i.e. make him sit or stand or even feed him, probably because he is technically supposed to be dead.