The lock screen does not update itself when the screen geometry changes. That can make it impossible to log back in. Reproducible: Always Steps to Reproduce: 1. Have an external screen connected to a laptop, and the internal screen turned off. 2. Suspend the machine 3. Plug off the external screen 4. Resume the machine Actual Results: The internal laptop screen shows a cursor, and is all black otherwise. Expected Results: The internal screen should show the lock screen. This is (another...) regression compared to KDE4.
This could be the same as bug #347934. Could you please check the xrandr output whether the information is correct?
This is really old, with few duplicates. Please reopen if it's still an issue.