drag-and-drop multiple items from a TreeView

[Jeff 'japhy' Pinyan <japhy perlmonk org>]

I've got drag-and-drop code working fine for moving ONE item at a time 
from one TreeView widget to another... but I can't get it to allow me to 
drag multiple items at once.

$l_tree->enable_model_drag_source(
  ['GDK_SHIFT_MASK', 'GDK_CONTROL_MASK', 'GDK_BUTTON1_MASK'],
  'GDK_ACTION_MOVE',
  $l_entry
);
$r_tree->enable_model_drag_dest('GDK_ACTION_MOVE', $l_entry);

The problem is not SELECTING multiple items (I have that taken care of), 
the problem is the widget is not dragging the items when I hold the left 
mouse button down when Shift or Control is pressed.

In fact, the GDK_*_MASK flags I'm passing don't appear to be doing 
anything at all.  I can replace them with just [], and the single-item 
drag works...

Any ideas?

--
Jeff "japhy" Pinyan         %  How can we ever be the sold short or
RPI Acacia Brother #734     %  the cheated, we who for every service
http://japhy.perlmonk.org/  %  have long ago been overpaid?
http://www.perlmonks.org/   %    -- Meister Eckhart