[flexcoders] Subclassing TileList breaks my code!?

[quiet.mountain]

Hi all,

This TileList was working fine:

<mx:TileList id="allYarnsTL"
     dataProvider="{allYarnsAC}">
        <mx:itemRenderer>
            <mx:Component>
                <mx:Canvas>
                    <mx:Image id="yarnImage"                    
                        source="{data.image}"/>
                </mx:Canvas>
            </mx:Component>
        </mx:itemRenderer>
</mx:TileList>

I then needed to override some TileList behaviours. So I started to 
subclass TileList...

package com.treelinerugs
{
        import mx.controls.TileList;

        public class TestTileList extends TileList
        {
                public function TestTileList()
                {
                        super();
                }
                
        }
}

and then created an instance as before...

<treeline:TestTileList id="allYarnsTL"
     dataProvider="{allYarnsAC}">
        <mx:itemRenderer>
            <mx:Component>
                <mx:Canvas>
                    <mx:Image id="yarnImage"                    
                        source="{data.image}"/>
                </mx:Canvas>
            </mx:Component>
        </mx:itemRenderer>
</treeline:TestTileList>

But now I get a compile-time error "Could not resolve 
<mx:itemRenderer> to a component implementation."

I can fix this by creating a separate component and creating the 
instance like this instead:

<treeline:TestTileList id="allYarnsTL"
     dataProvider="{allYarnsAC}"
     itemRenderer="com.treelinerugs.TLItemRenderer">

Why can't I define the itemRenderer in-line if I subclass TileList?

Thanks, Rich