(I first brought this up on the Dwarf Mode Discussion board, before I realized that it's probably counter to the designer's intentions:
http://www.bay12games.com/forum/index.php?topic=24869.0)
The issue arises when an animal is marked for butchering, and then assigned to a cage. I'm not sure if it has to happen in that order or not, but I brought it about twice through that method. (The caging was intended as a safeguard, just to keep a kitten from adopting an owner, in case it took the butcher a long time to get around to the task.)
After the butcher took possession of the cat and started hauling it to his workshop, a hauler pursued the butcher and took the cat away from him, and then the two of them began to take turns seizing the cat from one another. Contrary to my initial report on the other section, the struggle did not end when the hauler got the cat back into the cage; as soon as the butcher took it out, the battle was rejoined, and probably would have gone on indefinitely, until either I unassigned the cat from the cage, or until the butcher got away long enough to kill the cat.
It's actually pretty funny, but after a while you just want your dwarves to quit horsing around and get their asses back to work.
I made a video of it:
http://mkv25.net/dfma/movie-844-catfight. How's that for detailed bug reporting?
Oh, and since I'm reporting a negative, I'm going to counter that with a positive by adding that I love this game, and thanks for making it.