Beginner's confused concerning x & y after resize

programming flash
1

Hi

Can someone explian to my why, when I resize the window of the flash player the square does not remain in exactly the same place, ie 10,10.

And what I should do so that it does?

Thank you

package 
{
    import flash.display.BitmapData;
    import flash.display.Sprite;
    import flash.display.StageScaleMode;
    import flash.display.StageAlign;
    import flash.events.Event;
    
    /**
     * Example class to test the FluidBackground class.
     * @author Alan Jhonnes
     */
    public class FluidBackgroundExample extends Sprite 
    {
        public var square:Sprite = new Sprite();

        
        public function FluidBackgroundExample() {
            stage.align = StageAlign.TOP_LEFT;
            stage.scaleMode = StageScaleMode.NO_SCALE;
            
            
            square.graphics.beginFill(0x000000);
            square.graphics.drawRoundRect(10,10,100,stage.stageHeight - 200,10);
            square.graphics.endFill();
            
            stage.addChild(square);
            stage.addEventListener(Event.RESIZE, resizeListener);
            
            
        }
        
        public function resizeListener (e:Event):void {
            square.height = stage.stageHeight - 200;
//It doesnt stay at 10 with respect to the window... It moves down protionally as the window gets longer
            square.x = 10;
            
        }
    }
}

Thanks

Ward