Without the PPA this is because upstart runs unity and there is no synchronization between unity-gtk-module.service and unity7.conf.
With the PPA (i. e. converted services) this happens because unity-gtk-module.service stays running after killing X (systemctl restart lightdm) if there is another login. We need to restart it on login, or even better, ensure that it stops when X gets killed.
Without the PPA this is because upstart runs unity and there is no synchronization between unity-gtk- module. service and unity7.conf.
With the PPA (i. e. converted services) this happens because unity-gtk- module. service stays running after killing X (systemctl restart lightdm) if there is another login. We need to restart it on login, or even better, ensure that it stops when X gets killed.