Menubar disappears when space bar is pressed

[nico <nbd free fr>]

Hello,

I was developing and application with pyGtk and glade , under gnome 2.20.1 

And I have a funny behavior when I press the space bar. The menu bar
"moves out" of the application ( disappears) and is stored on the top
left of the desktop.

I not undestand where the problem is, and I try to use the space bar as
a key "short cut" on a button of the GUI. Somebody have an idea where
this problem come from ?

Here after the links "before/after" when the press of the space bar is done :
http://nbd.free.fr/gtk/capture_before.png
http://nbd.free.fr/gtk/capture_after.png

Thanks in advance.

Nico