[flexcoders] Simple but impossible Hbox alignment issue

[Flex Noob]

This one is rather perplexing. If I use a label inside an hbox and if the text 
inside the label runs too long it pushed the button off the screen:

    <mx:HBox width="100%">
        <mx:Label text="{text}"/>
        <mx:Spacer width="100%"/>
        <mx:Button id="button" width="20" height="15"/>
    </mx:HBox>

Doesn't Flex tell the label what is maxWidth should be so that doesn't 
happen????