[flexcoders] DataGrid extension does not render in FB3, why?

[fourctv]

Hi, I have subclassed DataGridColumn but it fails to render in FB3 design mode.
Everything works nice and dandy, it compiles and runs as expected.

But if I use my DGC in a DataGrid nothing shows up in FB3 in design mode.
Say I have a DG as:
   <mx:DG>
     <mx:columns>
        <mx:DGC/>
        <mx:DGC/>
        <my:myDGC/>
        <mxDGC/>
      </mx:columns>
    </mx:DG>


Only columns 1,2,4 show up in design mode on FB3.

 I tried to look into the framework's design.xml but found nothing related to 
DGC. And nothing in DG or DGC source seems to indicate any code that' specific 
to FB3 design rendering.

Any lead would be greatly appreciated.

TIA
julio