ActionScript 3.0 :: Two Sprite Objects - Adjusting Position (X And Y)

I am trying to do adjustment of position (x and y) of display objects, relative to other display objects. In other words: I have two Sprite objects (rectangle and circle). The rectangle can have their width changed during execution. Yet the circle has a fixed size. What I do is this: regardless of the width of the rectangle, the circle is positioned at the far right of this rectangle.

I tried as follows:
ActionScript Code:
rectangle.width = someValue;
circle.x = rectangle.x + (rectangle.width-circle.width);

In theory it should work, but look what happens:
imageshack.us/photo/my-images/837/positionq.png

As the width of the rectangle increases the distance from the desired location also increases.
Using:
ActionScript Code:
trace (rectangle.width);

I realized that the value of property 'width' does not match the exact amount of pixels that the object is wide. I just did a test and realized that this problem only happens when the rectangle has edge. When the rectangle has only fill, this problem does not occur.