It kind of sounds like a memory or video driver issue. What resolution is your document set at?
Mylenium is correct. When creating frame based animation each frame is linked to a layer. So to animate the motion of the selected portion it needs to be on new layers as it moves (each time you rotate or move, create a new layer. The smaller the increment the more layers needed, but will produce a smoother longer animation). The stationary portion(s) don't need to be on new layers because they are not moving and can be seen due to the transparent areas around the selection.
I hope that makes sense.