Distorted photo while scaling with tween

I’m trying to make a photo show with flash. Only I’ve got this one problem. A few photo’s distort or shake when I scale them with tween.
http://www.menkovic.nl/bouwding3/

Here is the .fla
http://www.menkovic.nl/bouwding3/main.fla

The swf isn’t scaled, it has a resolution of 640 by 480. I made the .fla on a mac but when I published it on a PC I’ve got the same problem.

Is there a solution for this problem or is it something flash just can’t handle?