GDBusObjectManagerClient ignores dbus signals after auto-activation
Under some conditions a newly created GDBusObjectManagerClient will not deliver g-properties-changed or interface-added signals after auto-activating a service.
The signals are received fine if the service was running before GDBusObjectManagerClient was instantiated. But if the service is auto-started by D-Bus because of the GetManagedObjects() call, the signals are not delivered on some systems... on other they work fine too. In all cases method calls still work Ok, only signals aren't delivered. It can be seen in dbus traces that the process does subscribe to all DBus signals from the org.freedesktop.DBus.ObjectManager interface using AddMatch().
I don't have a lot of information on this bug and I can't reproduce it in my machine but other people have had this problem for over a year and a half now, running different versions of glib, and it makes sense to start tracking this bug. The resulting NetworkManager problem is tracked at https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/101.