Hi,
I have the same issues, but since my anims also change the visibility of certain items(and they actually don't in Unity, latest runtimes 17 Jan 2017), I need both the bones and the slots to be refreshed.
So I need to call spineRenderer.skeleton.SetToSetupPose()
yet some props that shouldn't be visible still pop in for a frame. The animator got crazy keying all the animations for all the skins, but no success.
I'm also trying to call spineRenderer.skeleton.Update(<any value>) but has no effect today, it's still glitching.
How is possible this kind of issues still persist after a year? Am I doing something wrong?