Animating width of child rectangle in Layout container doesn't update other children

Hi,

Take the attached file as example.

In ASCII you have a layout like this:
-----------

-----------

"A" has a fixed width or even Layout.preferredWidth.
"B" fills up the available space.

If we change the width of "A" and animate that:
Behavior on width {
NumberAnimation

}

then "A" does animate to the new width. "B" however doesn't shrink/grow. It stays exactly as it was before the animation. So what happens here is "A" growing behind "B".

What should happen when A grows is B shrinks equally and the other way around.

I hope i explained it well.

Cheers,
Mark