When the "Enable menu shortcut key (F10)" option is disabled the menu still gets opened when you press F10. The only difference is that with the option disabled additional characters are sent to the terminal, and it prints the message "Gtk-CRITICAL **: gtk_device_grab_add: assertion `GDK_IS_DEVICE (device)' failed" to the parent console, if any.

This bug was reported for roxterm, in Debian and Arch Linux at least, but as it uses a similar technique to (try to) disable the menu as gnome-terminal I thought I'd try reporting it against g-t before GTK3 in case it's because we've both made a similar mistake and you might know how to fix it. roxterm-gtk2 is not affected, and it doesn't report the additional error message about gtk_device_grab_add.