Mask Duplicated MC not working

How come when I take a shape and make it duplicate with actionscript.

for (var i = 0; i<50; i++) {
	box.duplicateMovieClip(i, i);
}
for (var i = 0; i<25; i++) {
	box2.duplicateMovieClip(i, i);
}

the mask that i had over that shape stops working? Has anyone else had this happen. I could just put all the shapes on the stage and it works under the mask. But i think it is better to not have to lay out all the shapes so that is why i wanted to make them duplicate. C:-)