cacheAsBitmapの挙動

/**
 * Copyright barmamutha ( http://wonderfl.net/user/barmamutha )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/nwEY
 */

/*
 *参考http://barmamutha.net/?p=25
*/
package {
    import flash.display.Sprite;
    import org.libspark.betweenas3.BetweenAS3;
    import org.libspark.betweenas3.easing.*;
    import org.libspark.betweenas3.tweens.ITween;
    import org.libspark.betweenas3.tweens.ITweenGroup;
    [SWF(width="465", height="465", frameRate="60", backgroundColor="0x0")]
    public class Main extends Sprite {	
         public function Main() {
             var clip01:Clip = this.addChild(new Clip()) as Clip;
             clip01.x=10;
             clip01.y=10;
             var clip02:Clip = this.addChild(new Clip()) as Clip;
             clip02.x=10;
             clip02.y=70;
             clip02.blendMode = "layer";
             var clip03:Clip = this.addChild(new Clip()) as Clip;
             clip03.x=10;
             clip03.y=130;
             clip03.cacheAsBitmap = true;
             var clip04:Clip = this.addChild(new Clip()) as Clip;
             clip04.x=10;
             clip04.y=190;
             clip04.blendMode = "layer";
             clip04.cacheAsBitmap = true;
             var _t:ITween = BetweenAS3.parallel(
                BetweenAS3.tween(clip01, { alpha:0 },null,2),
                BetweenAS3.tween(clip02, { alpha:0 },null,2),
                BetweenAS3.tween(clip03, { alpha:0 },null,2),
                BetweenAS3.tween(clip04, { alpha:0 },null,2)
              );
              var _tGroup:ITweenGroup = BetweenAS3.serial(
                _t,BetweenAS3.reverse(_t));	
                _tGroup.stopOnComplete = false;	
                _tGroup.play(); 
         }
    }
}
import flash.display.Sprite;
import flash.display.Bitmap;
import flash.display.BitmapData;
class Clip extends Sprite{
    public function Clip(){	
        var _squareR = new BitmapData(50, 50, false, 0xff0000);	
        var _sqR:Bitmap = addChild(new Bitmap(_squareR)) as Bitmap;	
        var _squareW = new BitmapData(50, 50, false, 0xffffff);	
        var _sqW:Bitmap = addChild(new Bitmap(_squareW)) as Bitmap;	

     }
 }