AS3 joy and frustration

In the past few weeks I’ve been digging into the realms of the Actionscript world as much as I could. (And I was never as excited about any programming language before as I am about AS3.) I’ve been reading tons of documentations (primarily this one, several times), and still I have black spots even on pretty basic stuff.

For example, take this code:

package 
{
	import flash.display.Sprite;
	import flash.events.*;

	public class Main extends Sprite 
	{

		public function Main():void 
		{
			if (stage) init();
			else addEventListener(Event.ADDED_TO_STAGE, init);
		}

		private function init(e:Event = null):void 
		{
			removeEventListener(Event.ADDED_TO_STAGE, init);
			// entry point

			graphics.beginFill(0x7f7f7f);
			graphics.drawCircle(300, 300, 300);
			graphics.endFill();

			addEventListener(MouseEvent.MOUSE_MOVE, handler);
		}

		private function handler(e:MouseEvent):void
		{
			trace(e);
		}		
	}	
}

Seems pretty trivial, eh? The problem is that if I attach an event-listener to the main class of the swf file (as I did in the example above), seemingly no MouseEvent will be dispatched to the handler. If I add the very same event-listener to the stage, the mouse events suddenly start to be delievered.

Please, somebody educate me, why?