It seems a bug of as3 when using BitmapData.draw for a shape which is masked with another shape

Question

This is the code of my document class:
public class FirstMask extends Sprite
  private var maskedShape:Shape;
  public function FirstMask() {
   init();
  private function init():void {
   maskedShape = new Shape();
   addChild(maskedShape);
   maskedShape.graphics.beginFill(0xff0000);
   maskedShape.graphics.drawRect(0,0,80,80);
   maskedShape.graphics.endFill();
   var maskShape:Sprite=new Sprite();
   maskShape.graphics.beginFill(0x000000);
   maskShape.graphics.drawRect(0, 0, 20,20);
   maskShape.graphics.endFill();
   maskedShape.mask=maskShape;
   var bmd:BitmapData=new BitmapData(80,80);
   bmd.draw(maskedShape);
When I do not use the bmd to draw the maskedShape,everything is ok.When I do that,it seems the maskShape is auto-transformed including its position and size.As a result,I can not see the maskedShape unless I adjusted the IE size.Can anybody tell me why?
ps:If I set this.stage.align=StageAlign.TOP_LEFT; I can see the small scaled maskedShape.If I add the maskedShape to the displaylist ,everythis is ok.But Why drawing has the effect on the drawn shape?

Answer 1

Thanks again.But the "draw" itself is all right.
After " bmd.draw(maskedShape);",I code:
   var bm:Bitmap=new Bitmap(bmd);
   bm.x=100;
   bm.y=0;
   addChild(bm);
The bm can be shown.
So to make it clear,I print the screen:
1.No"mask" No "draw" at all.
2."mask" without "draw"
3."mask"and then "draw"---the IE shows nothing
4.If I drag the IE,adjust its size,then I can see a little thing on the top-left.
confusing...
PS:If I run the code as "air application",it seems all right.