Getting an error "tixGrid: mappedWindows not NULL" at program exit that I've been unable to avoid.

Program is adding Buttons to some cells of a TixGrid (where $cutgrid is a TixGrid) as in:
$cutbuttons{$y}{'cb'} = $cutgrid->Checkbutton(-background => 'white');
...
$cutgrid->set($x,$y, -itemtype => 'window', -widget => $cutbuttons{$y}{'cb'} );

If the buttons are not added, the error does not occur.

Have tried 'destroy' and 'UnmapWindow' on the $cutbuttons{$y}{'cb'} objects within a sub that gets called by the trapped 'WM_DELETE_WINDOW' event of the main window. These are all of the ideas I was able to find on the net.

Thanks for any help.