Sorry, but my attempts to reproduce it were to no avail. (Could you maybe add an option to have it log to syslog, instead? [AFAIK, GLog's default handler under Fremantle outputs to syslog.])
P.S. As a pedant and a GLib-whore lover, I have to ask to satisfy my feeling of nosiness: Why use the DBus-GLib bindings to provide the dbus-switchboard service but use the libdbus functions to listen to signals?