Client window resizing fuction problem

1

I have this snippet of code that allows the content of my stage to move along with the resizing of my browser window. It seems to work fine for the x coordinate, but when I resize the browser window vertically the movieclip doesn’t move with the browser window, and eventually disappears. Why is this working horizontally and not vertically?

sizeListener = new Object();
sizeListener.onResize = function(){

images_mc._x = Stage.width - 800;
images_mc._y = Stage.height/4

thumb1._x = Stage.width - 400;
thumb1._y = Stage.height/4;

};

Stage.addListener(sizeListener);