I've run LM13 with the Cairo Dock desktop on top of MATE - my default session on login is Cairo Dock (GNOME + effects) (am I right in thinking with this session I'm not actually in MATE?).
I've had an intermittent problem where when I open the laptop lid and the system resumes from sleep, the desktop wallpaper comes back up... and then nothing more - I don't get the prompt for my password, and so I can't get back to the desktop. The mouse pointer moves, but there's nothing to click. I've tried closing the lid again to put it back to sleep and tried again, with the same result. I've tried ctrl-alt-backspace but nothing happens.
All that does work is ctrl-alt-(a number) to switch to a TTY command prompt, from where I can run "sudo reboot".
I'm afraid I can't offer much in the way of anything which triggers this happening as it's only happened a small handful of times, but any clues what could be going on? Is there a way of "unblocking" it from a TTY prompt?