ActionScript 3.0 :: Push Items Into Movie Clip Failing?

I have an empty movie clip:

Code:
public var master:MovieClip = new MovieClip();

I'm trying to push items into this movieclip in a for loop:

Code:
for (var i:int = 0; i < panels.length(); i++)
{
var box:NavBox = new NavBox(800, 450);
box.x = box.width * i;
master.addChild(box);
}

It's not working. If I add the box to the stage, it'll work fine. But it won't go into the blank movie clip. No errors, just doesn't run.