How to prevent submenu closure after GtkCheckMenuItem toggling?

[Emmanuel Saracco <esaracco free fr>]

Hi,

I am searching a way to prevent submenu closure after a GtkCheckMenuItem 
has been toggled. I need that because my submenu display checkboxes used 
to filter a search result, and I don't want the user reopen menu/submenu 
every time he toggled one.

I trapped signals at GtkWidget level, but with no success.

Is there a way to do that, or is it currently impossible without 
creating a custom menu widget?

Bye