Surely #1, since we clearly test all Betas and we keep two installs (Standard and Beta) always installed, so we can switch back and forth to test if the issues are really caused by the Beta or not and if we need to do something to adapt to it.
When we are supposed to do something to be compatible with an undergoing beta and this can released without causing issues to non-Beta users, we do it, but in this case there was just nothing we could do, and the animation bug is affecting lots of other products so, it's just a plain bug and it's so big, that it couldn't possibly go unnoticed.