ActionScript 3.0 :: Get / Set Correct Height For Masked Object

I'm building a class for a data grid that creates everything dynamically, and allows the user to add buttons to a cell easily. If the user defines a height for the dataGrid that's smaller than the content, the content is cropped and a scrollbar is added. Now here's where my problem occurs. Once the content is masked, and you then try to access the .height property of the dataGrid, it will return the height of the dataGrid + the masked content.So I added a get/set override function for the .height property. Now this works, but only if I'm constantly updating the height as I create my dataGrid. What I'm curious about, is how (when the properties aren't overridden) when you add a child to a MovieClip, it's .height property is updated automatically? For example if you have

ActionScript Code:
var par:MovieClip = new MovieClip();
// each Cell is 20px tall.
var cell1:Cell = new Cell();
var cell2:Cell = new Cell();
par.addChild(cell1);
par.addChild(cell2);
trace(par.height);

The .height will equal 40px. Is there a set somewhere inside addChild that updates the .height property, or is there a different way that they do it? Basically I'd like to override the .height property after a certain amount of the dataGrid is built (to compensate for the difference in masked content height), but since the override happens from the very beginning, I'd like to know if there's a better way of setting my MCs height rather than constantly setting it as I build the grid. Or better yet, is there a way to get the proper height of an object that contains masked content without having to override the height?