Was just about to upload the gnome-screensaver fix and then I realised it doesn't work in this case:
When you switch users (e.g. to guest) indicator-session locks the screen then does the switch. With this change this causes lightdm to both start a greeter and a new session. I think the correct fix is for indicator-session to not attempt the lock when running under lightdm and get the lightdm daemon to always lock sessions when switching away from them.
Was just about to upload the gnome-screensaver fix and then I realised it doesn't work in this case:
When you switch users (e.g. to guest) indicator-session locks the screen then does the switch. With this change this causes lightdm to both start a greeter and a new session. I think the correct fix is for indicator-session to not attempt the lock when running under lightdm and get the lightdm daemon to always lock sessions when switching away from them.