This generic Autoreset isn't guaranteed to work when you have mixing.
I just looked into why, and the fix is ambiguous— there are a bunch of ways to go about it, both on the code side and on the animation data side.
I'll look into how it's supposed to work.
The short explanation if you're curious— and I encourage anyone to take a quick look at how this generic "Autoreset" works— is that the autoreset just tells the skeleton to refer to the setup pose and revert all its parts to it. This is done when a new animation starts. (AnimationState.Start).
The problem here is that after the new animation starts, the previous animation is still adding its changes and nothing is going to remove it.
Right now, the guaranteed way to make mixing work is to make sure all the keyed items in the "previous" animation are also keyed on the "next" animation. I know it's a bit complicated to do in the editor but there doesn't seem to be a way around that right now. But what you definitely shouldn't do is key everything. NEVER do that.
