[KumoKairo]

Таймер может вызываться чаще, чем фреймрейт. Простой тест:

package 
{
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.TimerEvent;
	import flash.utils.getTimer;
	import flash.utils.Timer;
 
	/**
	 * ...
	 * @author KumoKairo
	 */
	public class Main extends Sprite 
	{
		private var _prevEnterFrameTime:Number;
		private var _prevTimerTime:Number;
		private var _timer:Timer;
 
		public function Main():void 
		{
			if (stage) init();
			else addEventListener(Event.ADDED_TO_STAGE, init);
			addEventListener(Event.ENTER_FRAME, onEnterFrame);
			_prevEnterFrameTime = getTimer();
			_timer = new Timer(50);
			_timer.addEventListener(TimerEvent.TIMER, onTimer);
			_timer.start();
			_prevTimerTime = getTimer();
		}
 
		private function onTimer(e:TimerEvent):void 
		{
			trace("TIMER event: " + (getTimer() - _prevTimerTime));
			_prevTimerTime = getTimer();
		}
 
		private function init(e:Event = null):void 
		{
			removeEventListener(Event.ADDED_TO_STAGE, init);
			// entry point
		}
 
		private function onEnterFrame(e:Event):void
		{
			trace("ENTER_FRAME Event: " + (getTimer() - _prevEnterFrameTime));
			_prevEnterFrameTime = getTimer();
		}
 
	}
 
}

Output окно:

ENTER_FRAME Event: 203
TIMER event: 78
TIMER event: 62
TIMER event: 47
TIMER event: 47
ENTER_FRAME Event: 187

При частоте кадров 5 фпс.

Меняем до 60ти:

ENTER_FRAME Event: 15
ENTER_FRAME Event: 16
ENTER_FRAME Event: 31
TIMER event: 62
ENTER_FRAME Event: 31
ENTER_FRAME Event: 31
TIMER event: 62

Делаем нерекомендованное значение таймера 20 мс:

ENTER_FRAME Event: 31
TIMER event: 31
ENTER_FRAME Event: 32
TIMER event: 32

С неактивной флешкой:

ENTER_FRAME Event: 750
TIMER event: 749
ENTER_FRAME Event: 750
TIMER event: 750
ENTER_FRAME Event: 750
TIMER event: 750
ENTER_FRAME Event: 749
TIMER event: 749
ENTER_FRAME Event: 750