Scaling a masked movieclip

a while ago either senocular or eyezberg gave me an example of scaling a movie clip from a button with ease.
I have tried to use the movie clip I am scaling as a mask but every time i make it a mask all attempts to scale it by button no longer works.
Does anyone know why I can’t scale a masked movie clip?

http://www.zephn.com/scaler.zip is the source i am working with

bump… any pros know this one?