Why the background shrinks when my Car cross the STAGE?

programming flash
1

Hi,

I have the following code & one [COLOR=#ff0000]CAR [/COLOR]which moves from [COLOR=#0000ff]right to left[/COLOR]. When the CAR moves out of the stage, the background gets shrink. How to solve this problem?

The Code:

var myStage:Stage=this.stage;
myStage.scaleMode=StageScaleMode.NO_SCALE;
myStage.align=StageAlign.TOP_LEFT;


function initialDisplay(event:Event):void{
	var swfWidth:int=myStage.stageWidth;
	var swfHeight:int=myStage.stageHeight;
	
	Background.width=swfWidth;
	Background.height=swfHeight;
}


addEventListener(Event.ENTER_FRAME,initialDisplay);

Note: There is no other code except the above one. Car moves by Classic Tween.

The FLA file size is 6.26 MB. So I cannot attach it. But the jpg file illustrates my problem.

Thanks for any help.