[gtkmm] Problem dynamically adding to a VBox

[RMM <morelli cs utah edu>]

I have a VBox to which I add an EventBox.  The EventBox contains
a bunch of other widgets that together constitute the board of
a puzzle game.  When I add the EventBox before the VBox is realized,  
everything works fine.  However,  if I add the EventBox after the
VBox is realized,  the board appears but it doesn't usually respond 
to mouse button presses.  (It responds about 1 in 5 times I launch
the application.)  Can someone give me a hint about what's going
on?