ADDED event in document class after removed from Stage

Hi All,

I am currently play with the document class (the class acts as main) constructor for a SWF file.

package {

  import flash.display.*;

  import flash.events.*;

  public class TestSymbol extends MovieClip

  {

    public function TestSymbol()

    {

      this.addEventListener(Event.ADDED, function(event:Event) { trace(event.eventPhase, event.target, event.currentTarget, "added triggered"); });

      trace("parent", this.parent);

      this.stage.removeChild(this);

      trace("stage", this.stage);

    }

  }

}

In frame script 1, i put

trace("1");

trace("parent", this.parent);

After i run TestSymbol.swf and  i got

parent [object Stage]

stage null

2 [object TestSymbol] [object TestSymbol] added triggered

1

parent null

I wonder where is this ADDED event coming from? If the document class is added to some other objects, why its parent is null after the event?

Thanks in advance

Sam