GC не срабатывает

[artcraft]

не удаляется экземпляр класса :~/
в чём причина?

так работает:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.TimerEvent;
	import flash.utils.Timer;

	public class Test extends Sprite {
		
		function Test():void {
			var a:Sprite = new Sprite();
			a.addEventListener(Event.ENTER_FRAME, efListner, false, 0, true);			
			addChild(a);removeChild(a);a=null;
			
			function efListner(e:Event):void {trace('Please delete me...');}
			
			forceGCRun();
		}
		
		
		private function forceGCRun():void{
			var a:Sprite;
			var count:uint;
			var oldCount:uint;
			var timer:Timer;
			
			a = new Sprite();
			a.addEventListener(Event.ENTER_FRAME, efListner, false, 0, true);			
			addChild(a);removeChild(a);a=null;
			function efListner(e:Event):void {count++;}

			timer = new Timer(1000);
			timer.addEventListener("timer", timerHandler, false, 0, true);
			timer.start();
			
			function timerHandler(e:TimerEvent):void {
				if(oldCount == count){
					 trace(':)', timer.currentCount);
					 timer.stop(); timer=null;
				}
				oldCount = count;
				for (var n:uint=0; n<10000; n++){
					a = new Sprite();	addChild(a);removeChild(a);a=null;
				}
			}
		}
				

	}
}

а так не работает:

package{	
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.TimerEvent;
	import flash.utils.Timer;
	
	public class Test extends Sprite{	
	
		function Test(){
			
			var c:c1 = new c1();
			addChild(c); removeChild(c);
			c=null;
			
			forceGCRun();
		}
		
		public function forceGCRun():void{
			var a:Sprite;
			var count:uint;
			var oldCount:uint;
			var timer:Timer;
			
			a = new Sprite();
			a.addEventListener(Event.ENTER_FRAME, efListner, false, 0, true);			
			addChild(a);removeChild(a);a=null;
			function efListner(e:Event):void {count++;}

			timer = new Timer(1000);
			timer.addEventListener("timer", timerHandler, false, 0, true);
			timer.start();
			
			function timerHandler(e:TimerEvent):void {
				if(oldCount == count){
					 trace('GC RUN :)', timer.currentCount);
					 timer.stop(); timer=null;
				}
				oldCount = count;
				for (var n:uint=0; n<10000; n++){
					a = new Sprite();	addChild(a);removeChild(a);a=null;
				}
			}
		}
	

	}
}

import flash.display.Sprite;
import flash.events.Event;

class c1 extends Sprite{
	function c1(){
		addEventListener(Event.ENTER_FRAME, function(e:Event):void{trace('c');},false,0,true);
	}
}