Zooming ListBox issue

Hi!

I have a android air application that has a listbox witch you can zoom with touch.

But there are an issue with that that i can't solve:

List with no zoom:

List with zoom:

As you can see, the first listbox cell has much height than the other ones (and the x/y coordinates are diferent).

The code to zoom the list box is that:

function onZoom(e:TransformGestureEvent):void {
  if(touchList.scaleX>0.8 && touchList.scaleX<1.5)
  {
       touchList.scaleX *= (e.scaleX+e.scaleY)/2; 
       touchList.scaleY *= (e.scaleX+e.scaleY)/2;
  }
  else if (touchList.scaleX<0.8)
  {
       touchList.scaleX = 0.801; 
       touchList.scaleY =touchList.scaleX;
  }
  else if (touchList.scaleX>1.5)
  {
       touchList.scaleX = 1.499; 
       touchList.scaleY =touchList.scaleX; 
  }
  }

How could i scale the listbox keeping an equal cell height and without changing the x,y positions?

Thank you very much