abuki To mix back to the setup pose, set an empty animation with no mix duration. The note about needing one more frame when mix duration is zero is trying to explain that it will take one more apply
to do the mixing out, and then the update
after that will be able to "end" the track entry (the end
AnimationStateListener event).
You don't normally need to worry about this. You just set the empty animation and continue on as normal.