I've successfully installed the MATE desktop 1.6 on Ubuntu 13.04 64Bit. When I log on to my system, I have only two sessions to choose from: Ubuntu, and Mate (Ubuntu includes the Unity launcher). All is well, including Compiz (pleasantly surprised to find out it maintains separate settings for each session).
I have the Variety wallpaper changer running in both sessions, all running well. Tiny glich:
1. I'm logged in to Ubuntu/Unity, log out, and the login screen has the last active wallpaper as a background, as expected, since that's how I set up Variety to work.
2. Log in to MATE. Log out. Now the login screen has the default Ubuntu ugly purple/orange smear.
3. Log in again, to Ubuntu/Unity. Log out. Now the login screen has, again, the last active wallpaper as background.
4. Repeat #2 above, same result.
It appears the last active wallpaper is preserved as login-screen wallpaper only after coming out of an Ubuntu/Unity session, but not after coming out of a MATE session.
For what it's worth, I know exactly how Variety saves that last active wallpaper - in the /Home/Pictures folder, as something like "copied-variety-etc-etc-xxx" where xxx is in fact a 32-character hex value.
I also found out, that MATE also saves the last active wallpaper, in /home/.cache/mate/background, but it doesn't use it for the login screen where I log out of a MATE session.
If I could enter a setting in lightdm.conf to put a specific wallpaper on the lightdm greeter, that would be peachy. I don't need it to cycle, I could disable that feature in Variety.
Note however, that when I lock the screen, whether under gnome or mate, THAT login screen gets the last active wallpaper ok. But not the lightdm greeter when logging out of mate.
I should note, I've already tried the lightdm wiki, it's either out of date or talking about a different flavor of Ubuntu (Lubuntu perhaps?), because it refers to /etc/lightdm/lightdm-gtk-greeter.conf which doesn't exist on my system (here it's /etc/lightdm/lightdm.conf) and the setting they give simply had no effect.
Any ideas? No offense to anyone, but that orange-purple-the-sixties-just-called atrocity is making my eyes bleed.