Well, just a hint: Mixing absolute pixel- and relative sizes cannot work per definition. If your browser-window is wider than 600px, your AbsoluteLayout will always be smaller than the Panel. Don’t know about AbsoluteLayout as I never used it - but you should set the width of the layout in relative matters too. If that doesn’t help, try to set the expand-ratio to 1 and / or add the AbsoluteLayout as Content (setContent) instead as (sub-)component (addComponent).
Then you could finally use firebug and try to inspect the generated HTML, maybe you find something interesting there.