3D shadows / Depth of field

3D shadows with setMask . Help needed
I have a movieClip instances that i have applied a blur to. I have then tried to mask the movieClip with the following:

myMovieClip_mc.setMask(myMask_mc);

I’ve also tried setting: cache the mask as Bitmap True as well as false.

But what appears to be happening is that the blur is applied to both the mask and the movie clip. So the end result is softening the edge of the mask which is not the effect I was aiming for.

Anyone got any ideas?