I'm running an Openbox session in Lubuntu 13.04 with the same lxpanel as I do in a standard Lubuntu session because I prefer that rather than the "right-click" menu provided in the Openbox session.

I notice that lxpanel's Menu lists some applications twice in an Openbox session but just once in a Lubuntu session. Digging a little more, I get the impression it is because the "OnlyShowIn" and "NotShowIn" instructions in certain .desktop files (in /usr/share/applications) are being ignored in an Openbox session.

For example, I have two "Software & Updates" .desktop files:

-rw-r--r--   1 root root   466 Jun  7 00:51 software-properties-gnome.desktop

-rw-r--r--   1 root root   531 Jun  7 00:51 software-properties-gtk.desktop

The upper one has OnlyShowIn=GNOME;

and the lower one has NotShowIn=GNOME;

Both are visible in an Openbox session but only the latter appears, and correctly so, in a Lubuntu session. Is it because an Openbox session isn't a "desktop environment" and is not listed in Registered OnlyShowIn Environments?

(It's not just about GNOME. I also have two Synaptic Package Manager .desktop files; one has OnlyShowIn=KDE; it is visible in the Openbox session but is not seen in the Lubuntu session.)