Window(manager) border inconsistency

[RNG <r gasch chello nl>]

Hi, 

I have a Gtk-- (C++ wrapper) based application which is mysteriously 
displaying differences in the way the window manager decorates/frames 
the window. The Gtk-- folks suggested I ask here as they;re not sure 
either: 


While playing around with my app, I've noticed that depending on 
if I have a popup menu vs. a traditional menu, the window border (as 
generated by the window manager) differs. To see what I mean, take 
a look at 

 http://212.187.12.197/gtk--bug/

Does anybody have any ideas what might be causing this? I'm not 
aware of anything in my code that I would hold accountable for this 
difference. The interesting thing though is, that I don't seem to have 
any code in my application which sets any WM hints. Could this be an
inadvertant result of something else I'm doing (ie: > setting styles, etc.)?


Thanks
--> Robert