CS3 Unknown bug?

I was creating a form and when i exported them movie it was 400+ kb i redo another 1 and it was only 105Kb. Anyone know what is going on here ???

additional :

form 1 (400+ kb)
200 frames of introduction @ 24 FPS
a movie clip containing all the form components

note: even when i deleted everything in the stage(layers of images), it was still 400+ kb. WEIRD ?!

form 2 (redone, 105kb)
200 frames of introduction @ 24 FPS
no movie clip for form components.