Tweening a Rounded Rectangle in Actionscript 3

Question

I would like to tween between a short rounded rectangle and a tall rounded rectangle. (I only want deal with the height - no other parameters). I am programming with ActionScript 3. My tweening engine is TweenLite.
I have been tweening a sprite that contains a rounded rectangle. The tweened sprite produces distortion. I suppose that I have been scaling the original image, rather than the height of the rounded rectangle?
Here is a simple example of my code:
Draw the rounded rectangle:
roundRect = new Sprite();
roundRect.graphics.beginFill(0x000000);
roundRect.graphics.drawRoundRect(0,0,50,15,4,4); //Original Height: 15
roundRect.graphics.endFill();
addChild(roundRect);
Then I listen for a mouse click event on the rounded rectangle.
The mouse event triggers a function with the following code:
TweenLite.to(this.roundRect, 1, {height:120}); //Final Height: 120
I would like to tween the height of the rounded rectangle itself. I would hope that this would not produce the unwanted distortion. Is there any way to achieve this?
Thank you.

Answer 1

Ned,
Thank you for your response.  I apologize for the delay in my own response.
I was seeing distortion in x direction as well.
I was able to solve my problem using 9-slice scaling.  I used the scale9Grid property.