[flexcoders] Flex 4 HGroup and Group background colour

[bhaq1972]

Why does this work 

<s:Group width="100%" height="28">
   <s:Rect top="0" right="0" bottom="0" left="0">
        <s:fill>
          <s:SolidColor color="0x4960a6" />
        </s:fill>
   </s:Rect>
</s:Group>

But this doesnt?
<s:HGroup width="100%" height="28">
  <s:Rect>
    <s:fill>
      <s:SolidColor color="0x4960a6" />
    </s:fill>
   </s:Rect>
</s:HGroup>

thanks