Thanks for the hint Neal - I checked it out in Synaptic for future reference. Now the bad news - the problem has fixed itself. I hate it when that happens! I've had it happen before once or twice, but this time it really persisted and I thought I had borked something. Now I know where to go if it happens again.
Hi Taco and Neal,
Reinstalling openbox-menu has no effect on right-click menu, because openbox-menu is just a pipe-menu. It is the libe menu-cache (Lxde project) which does the job. To regenerate a right-click menu that has gone, or even to refresh it after you uninstall a program or install a new one, generally trying to display it twice on a row does the trick.
To avoid loosing the whole "Applications" right-click menu, check in your Bleachbit preferences config that the directory and files from ~/.cache/menus/* are added to the whitelist (it must be added in order to prevent Bleachbit from removing them when you operate a cleaning).
In case you want a fast fix, you can copy the cached files from /etc/skel/.cache/menus, or from /root/.cache/menus :
in this case, you should check that the ownership of the files be your user (and correct it if the cached menu files still belong to root after the copy).
Last : have you checked the new set of configuration files in /usr/share/openbox-menu after the last update ?