Is it a BUG or something else? Can't Capture Mouse E

Just try the below code:

package  
{
	import flash.display.*;
	import flash.events.*;
	import flash.net.*;
	
	public class main extends MovieClip
	{
		private var _file:String = "stickers/dirt_road.swf";
		private var _ldr:Loader;
		private var _sticker:MovieClip;
		
		
		public function main() 
		{
			this.addEventListener(Event.ADDED_TO_STAGE,this.addedToStageHandler);
		}
		
		
		private function addedToStageHandler($e:Event):void
		{
			var $req:URLRequest = new URLRequest(this._file);
			this._ldr = new Loader();
			this._ldr.contentLoaderInfo.addEventListener(Event.COMPLETE,this.loaderHandler);
			this._ldr.load($req);
		}
		
		
		private function loaderHandler($e:Event):void
		{
			//trace($e.target.content);	//[object MovieClip]
			this._sticker = $e.target.content as MovieClip;
			this.addChild(this._sticker);
			this._sticker.addEventListener(MouseEvent.MOUSE_DOWN,this.stickerMouseDownHandler);
		}
		
		
		private function stickerMouseDownHandler($e:MouseEvent):void
		{
			trace("Vince");	// never be executed
		}
		
	}
	
}

And you would find the handling method would nevre be invoked. Someone already reported the same problem:

http://board.flashkit.com/board/showthread.php?735451-Can-t-capture-mouse-events-on-a-loaded-swf