I recently installed Sparky LXDE 4.5.2x86_64 and replaced lxpanel with fbpanel. Everything works fine except all the items in the fbpanel menu appear twice. Searching shows this is not a new issue with Linux menus in general. Does anyone know a solution without replacing fbpanel-menu? I can circumvent the problem by removing the fbpanel menu and adding another menu, for example, the Lxde menu, as a panel application. Such menus will be correct, but I am curious what (maybe lxsession?) is monkeying with the fbpanel menu here. No app that I tested appeared to have more than 1 .desktop file on the computer.
(http://lxlinux.com/double.png)
Moving all the .desktop-files from /usr/share/applications to ~/.local/share/applications changed the double entries in fbpanel-menu to single entries which temporarily solved that problem. I say "temporarily" because as soon as a new app is installed with its .desktop file placed in /usr/share/applications, which is the usual thing, then that app is given a double entry in the menu. For the record, moving the .desktop-files to /usr/local/share/applications also produces a double entry.
Apparently the fbpanel menu, which is not constructed, like most other panel menus, from an application .menu file in /etc/xdg/menus, is constructed by processes built into the desktop. So with multiple desktops installed, it may (or may not) be built multiple times (duplicate entries). Sparky-lxde comes with openbox-lxde-session. Booting into an lxde session activates both to populate the fbpanel menu. Booting into just an openbox-session only populates the menu once.