How to not use the "Space bar" as default key ?

[nico <nbd free fr>]

Hello,
I am developping an application under ubuntu/gnome, I use pygtk and glade.

On my application the "space bar" acts like the "return key" , so as a
default key. So when I press the "space bar" the button under the focus
is clicked (signal emited) .
I want to use the "space bar' for activation of a specific button, not
for the button currently under the focus. How I can set a behavior like
this ?

Thanks in advance
Nico.