Flex 4: Build a Group with a background

I'm trying to build a simple component extending spark.components.Group to have a background color, more specifically a spark.primitives.Rect component stretched to fill the background.

This is what I've come up with thus far:

<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo"
    <fx:Metadata>
        [DefaultProperty(name="content")]
    </fx:Metadata>

    <s:Rect id="background" width="100%" height="100%">
        <s:fill>
            <s:SolidColor color="#990000"/>
        </s:fill>
    </s:Rect>

    <s:Group id="container"/>

    <s:filters>
        <!-- For good measure ;) -->
        <s:DropShadowFilter color="#000000" strength="0.4" blurX="5" blurY="5" distance="2" angle="90"/>
    </s:filters>

    <fx:Script>
        <![CDATA[
            public function set content(value:Array):void {
                this.container.mxmlContent = value;
            }
        ]]>
    </fx:Script>
</s:Group>

Ok, so the logic here basically makes sense, right? All children declared in MXML go to the Group called "container". That is working just fine. However, when I run the example below, the layout is completely fubar.

<s:VGroup>
    <!-- This is the component described above -->
    <components:MessageContainer id="component" width="100" height="100"/>
    <mx:Slider/>
    <开发者_StackOverflow中文版mx:Slider/>
    <mx:ColorPicker/>
</s:VGroup>

This is what it looks like:

Is there something I'm missing here? Maybe a method I need to override?

Weird. I just resorted to making a Skin implementation and applying it to a SkinnableContainer. I was compiling using the Beta 2 release of Flex 4 as well. Very strange indeed.

What build of flex 4 are you using? I just copied your code exactly and the output looks as you would expect it to.

I am running the beta 2 build that was released within the last few weeks. Build 4.0.0.253292. You can upgrade your build if you aren't running the latest, but you can also try to clean the project. It might just be getting confused. Also make sure your browser isn't caching the swf, which sometimes happens when the file size doesn't change dramatically.