9scale will not work with mask

Hi all
been trying to use the 9scale feature on a moviclip that change its size
according to an image being loaded
and then setting it as a mask to the content

the clip 9scale feature works as expected
as long as it's not a mask

did any of you tried any of the sort ?

for example
a gallery
loading an external image into a clip
i want the frame of the image to be a rounded edges rectangle
therefore i use a clip to set the mask
which suppose to scale itself according to the image being loaded
9scale will not work niether with a ui layer mask
nor with a setMask( ) unfortunatly
here is the code
on the stage are the clips
set to 9scale mode in the properties via the library

thanks
yariv


//set width according to the image loaded
//setMask doesn't work
var mcl:MovieClipLoader = new MovieClipLoader();
var l:Object = new Object()
l.onLoadInit = function(target:MovieClip) {
//trace(target._width)
target._parent.bg_mc._width = target._width + 15;
target._parent.mask_mc._width = target._width ;
target.setMask(target._parent.mask_mc)
}
mcl.addListener(l)
mcl.loadClip("collaborate.jpg",container_mc)