It's just a coincidence: I had N900 running for several days without reboot while trying to make the plugin; as soon as the plugin was created, I allowed myself to turn it off for the night; [supposedly, during this several days something messed with DBus]; start up in the morning showed something is wrong; after several reboots and typing some commands (like env, osso-product-info, gconftool) it became clear that something is wrong with DBus (corrupted files, wrong permissions, don't know), DBus was reinstalled, and after reboot everything became perfect and smooth.

It could be just result of my inclination to type chmod 0777 for any directory I see, but I don't remember touching DBus in any way.

In any case, now I'm trying to make this plugin not only usable, but also useful.

P.S. I would advise to have separate mbarcode package, mbarcode plugins packages (depending on mbarcode) and mbarcode-all package (empty; no code, just dependencies), which just depends on mbarcode and the plugins which are useful. Then user could choose whether to install mbarcode-all and get all plugins automatically through dependencies, or to install mbarcode and choose plugins manually. Just my opinion.