This happened to my friend twice in one week. He tames beefalos a lot, and he found that when you hop onto a beefalo in the middle of its domestic transformation, it will bug out and the beefalo will not behave like a tamed beefalo. It will look untamed (scruffy fur) when you're not riding it, but when you hop on it, it will look tamed (the clean fur). It will still be able to shake its saddle off - which domesticated beefalos are not normally able do. Also it was supposed to be ornery, but because of the bug, the beefalo still does the base 34 damage.
hop onto beefalo during its domestic transformation. idk how to do this easily in practice game.