Why is it that, when I enable dragging-and-dropping in a TitleGrid, items are copied when they are dragged instead of moved?
For example:
<mx:TileList dragEnabled="true" dropEnabled="true">
    <mx:dataProvider>
        <mx:Array>
            <mx:Object label="Nokia 6630"/>
            <mx:Object label="Nokia 6680"/>
        </mx:Array>
    </mx:dataProvider>
</mx:TileList>
When either of those items is clicked-and-dragged, it will get copied instead of moved.
This is especially confusing because TileList is a decedent of ListBase, which DataGrid also descends from... But DataGrid does the right thing when dragging and dropping items.