Ah, maybe you have the "menu bar" applet turned on in gnome-panel?
Originally Posted by Robor
You need to find the script where gnome-panel is launched, and set environment variable GTK_MENUBAR_NO_MAC=1. Or you could start gnome by a manual ~/.xinitrc:
Remove the "menu bar" plugin, then remove the "GTK_MENUBAR_NO_MAC=1", and restart gnome.
GTK_MENUBAR_NO_MAC=1 exec gnome-panel
(if you start gnome-panel with GTK_MENUBAR_NO_MAC=1, all apps launched from the panel wouldn't show the mac menubar)