AIR issue: buzzing/flickering while animating alpha

Steps to reproduce:
1.compile and debug the following:
package
{
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.Sprite;
import flash.events.Event;

public class FadeTest extends Sprite
{
protected var b1:Bitmap;
protected var b2:Bitmap;
protected var containingSprite:Sprite;
protected var currentAlpha:int = 255;

public function FadeTest()

{ containingSprite = new Sprite(); b1 = createBitmap(); b2 = createBitmap(); addChild(containingSprite); containingSprite.addChild(b1); containingSprite.addChild(b2); addEventListener("enterFrame", onEnterFrame); }

protected function createBitmap():Bitmap

{ var data:BitmapData = new BitmapData(200,200,false,0x3F3F3F); var bitmap:Bitmap = new Bitmap(data); return bitmap; }

protected function onEnterFrame(e:Event):void

{ // Sample pixel of current representation var bmd:BitmapData = new BitmapData(200,200,true, 0); bmd.draw(containingSprite); trace("sample pixel is " + bmd.getPixel(0,0) + ", should be " + 0x3F3F3F); // Continue fade of b1 bitmap. currentAlpha = (currentAlpha <= 0) ? 255: currentAlpha; b2.alpha = currentAlpha / 255.0; currentAlpha -= 1; }

}
}

2.
3.

Actual Results:
sample pixel is 4144959, should be 4144959
sample pixel is 4144959, should be 4144959
sample pixel is 4079166, should be 4144959
sample pixel is 4079166, should be 4144959

Expected Results:

Workaround (if any):