Silly me, I had overlooked the fact that we aren't using the same greeter. I've got [SeatDefaults]greeter-session=unity-greeter in /etc/lightdm/lightdm.conf. So of course your solution didn't work for me. (I need to give users a choice of desktop sessions, and found unity-greeter to be better at remembering a user's last session.)
You may have found a valid workaround for GTK greeter users; unfortunately I cannot switch to it.
Silly me, I had overlooked the fact that we aren't using the same greeter. I've got [SeatDefaults] greeter- session= unity-greeter in /etc/lightdm/ lightdm. conf. So of course your solution didn't work for me. (I need to give users a choice of desktop sessions, and found unity-greeter to be better at remembering a user's last session.)
You may have found a valid workaround for GTK greeter users; unfortunately I cannot switch to it.