poking at some of the shell networking code and ran into this again:

            // Need to go through GObject.Object.prototype because
            // nm_device_disconnect conflicts with g_signal_disconnect
            GObject.Object.prototype.disconnect.call(this.device, this._stateChangedId);
            this._stateChangedId = 0;

And this isn't really an isolated case; of the girs I currently have installed, there's:

  cd_client_connect
  cd_device_connect
  cd_profile_connect
  cd_sensor_connect
  g_cancellable_connect
  g_cancellable_disconnect
  gda_thread_wrapper_disconnect
  g_proxy_connect
  g_socket_client_connect
  g_socket_connect
  g_socket_connection_connect
  gtk_accel_group_connect
  gtk_accel_group_connect
  gtk_accel_group_disconnect
  gtk_accel_group_disconnect
  nm_device_disconnect
  soup_server_disconnect
  soup_socket_disconnect
  tp_proxy_signal_connection_disconnect

Maybe the signal methods ought to be ".signal_connect" and ".signal_disconnect"? Or at least add those as aliases, so they're available when the normal names get shadowed.