Parental Guidance Needed!

I have a main MC, on which I have a button which dynamically loads another MC on top (like a popup).
On this popup, I have a close button, which works.
On the popup, I have another button which dynamically loads another MC on top of popup #1.
I cannot get the close button on popup #2 to close just that popup, it either does not work at all, or closes both #1 & #2 at the same time.
I know it has to do with hierarchy, but just cannot grasp this method.
Attached is the code & files.

 
//*************
//pop1 MC
//load mcPop2 on top of pop1 and main
var parent:MovieClip = this;
btnPop2.onRelease = function (){
parent.createEmptyMovieClip('holder', parent.getNextHighestDepth());
loadMovie('mcPop2.swf', holder);
holder._x = 50;
holder._y = 100;
}
 
//pop1 close button
//close pop1 only
on(release){
_root.holder.unloadMovie();
}
//*************
//pop2 MC
//close pop2 only... leave pop1 on top of main
on(release){
_root.holder.unloadMovie();
 
}
 
 

Files: http://downeydesign.com/swfs/poptest.zip