I'm using xubuntu 14.04 on AMD based hardware. It is configured not to lock a session and not to power down automatically on longer idle times.
There have been no recent changes or new software installations other than notified security updates.
I also have the kde desktop installed. The display manager is LightDM, AFAIK.
The system has been behaving nicely for some months, until a couple of days ago. Now, after about ten minutes idle the session is locked automatically. The screen presents a dialog with the caption "This session is locked".
Attempting to "unlock" with the session's username and password results with the message
"You'll be redirected to the unlock dialog in a few seconds" and the cycle starts over. Unable to log in, the only option seems to be to reboot. (I won't mention the work I have just lost":-( )
Does anyone have any idea what's going on here, bearing in mind that AFAIK the power managers are configured NOT to lock sessions and not to power down on idle?