Comment 13 for bug 1546641

https://git.gnome.org/browse/gnome-settings-daemon/tree/plugins/power/gsd-power-manager.c#n2589 checks whether the computer has a lid before it queries the status for it. But unity-settings-daemon apparently did not get that fix yet as per the StacktraceSource.txt attachment:

 3323: manager->priv->up_client = up_client_new ();
 3324: manager->priv->lid_is_closed = up_client_get_lid_is_closed (manager->priv->up_client);

This code was introduced into g-s-d in 2013, but got it right immediately: https://git.gnome.org/browse/gnome-settings-daemon/commit/?id=ddfef4e8

So I figure u-s-d got some deviating development in this area.