GtkOptionMenu menu is invisible

[rob <mailingLists pangolin org uk>]

Hi I'm haveing problems with GtkOptionMenu I'm trying to set the menu
that it pops up like so:

        newModeMenu = GTK_MENU(gtk_menu_new());
        for (i = 0; i < scaleType_get_noModes(scaleType); i++){
                gchar *modeName;
                GtkWidget *menuItem;

                modeName = scaleType_get_modeName(scaleType, i);
                menuItem = gtk_menu_item_new_with_label (modeName);
                gtk_menu_append(newModeMenu, menuItem);
                g_free (modeName);
        }

        modeOM = GTK_OPTION_MENU (lookup_widget (scaleWindow, 
                                                 "scaleModeOM"));
        gtk_option_menu_remove_menu(modeOM);    
        gtk_option_menu_set_menu (modeOM, GTK_WIDGET(newModeMenu));

And though it all seems to work,when the option menu is clicked no menu
is shown just a tiny little square.
I can call gtk_option_menu_get_menu look at the menu and it all seems
correct and the lable in the option menu itself is correct (it is the
first menu item.)
Am I doing something obviously wrong here?
I tride sticking in a gtk_widget_show but it didn't help.

This is on debian potatoe with ximian gnome. The option menu is
orgionall created by glade.

Thanks 
-- 

rob