GtkSeparatorMenuItem looks wrong (Gtk3, Python3)

[David Rawson Couzelis <drcouzelis gmail com>]

The GtkSeparatorMenuItem widgets in the menubar of my application look
wrong. There should be a horizontal line separating the menu items, but
instead, there is only an empty space. In other words, there's a space
separating the two menu items, but there's no horizontal line.

Could this be a bug? Or, am I using the GtkSeparatorMenuItem incorrectly?

I'm using Gtk 3.2.3 and Python 3.2.2.

Below is a simple example showing how to reproduce the problem.

Thank you,
Dave

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from gi.repository import Gtk

menu = Gtk.Menu()
menu.append(Gtk.MenuItem('New'))
# The following separator menu item looks wrong :'(
menu.append(Gtk.SeparatorMenuItem())
menu.append(Gtk.MenuItem('Quit'))

menuitem = Gtk.MenuItem('File')
menuitem.set_submenu(menu)

menubar = Gtk.MenuBar()
menubar.append(menuitem)

vbox = Gtk.VBox()
vbox.pack_start(menubar, False, True, 0)

def on_closed(widget, data):
    Gtk.main_quit()

window = Gtk.Window()
window.resize(400, 300)
window.add(vbox)
window.connect('delete-event', on_closed)
window.show_all()
Gtk.main()