[flexcoders] MouseOver Event Not Firing

[Geoffrey]

I have a Button that doesn't seem to know the mouse is over it.  It 
doesn't dispatch MouseOver/Out/click events.

I have a Panel that has an HBox(Label/Spacer/Button) and a Canvas.  
the Canvas gets stuff added to it dynamically via Actionscript.

<pre>
<mx:Panel xmlns:mx="http://www.adobe.com/2006/mxml"; width="100%" 
height="100%">

  <mx:HBox id="titleBox" verticalAlign="middle" width="100%" 
height="24">
    <mx:Label text="Your Tasks"/>
    <mx:Spacer width="100%"/>
    <mx:Button id="backButton" click="onClick(event)" width="24" 
height="20"/>
  </mx:HBox>

  <mx:Canvas id="dynamicContainer" width="100%" height="100%"/>

</mx:Panel>
</pre>

This component is displayed after a transition effect that 'swishes' 
it in from the right.  I've done some debugging and it seems that 
everything is getting mouseOver events except everything within the 
HBox.

Any ideas?  Because I have run out of ideas.

Thanks,
Geoff