Going backward and forward in my timeline

Hi,
I have an animation of a rotating 3d object, and I’m playing it backward and forward through simple nextFrame() and prevFrame() actions inside an onEnterFrame event.
Everything seems to work, the only technical problem is that if I go backward, the animation is not as smooth as if I went forward. I understand that a prevFrame action is ‘less natural’ than a nextFrame… but does anyone know how I could fix it?

here is my source (compile the fla to see what I mean)
http://www.albertomarcone.com/lavoro/test3d.zip

thank you in advance.