package: xserver-xorg-core version: 2:1.19.2-1+deb9u2 severity: important
The laptop was being used with a Thunderbolt 3 dock. The lid was down while it was being used and the display attached to the dock was the only active display. The sleep button was pressed on the dock and the laptop went to sleep. The Thunderbolt 3 cable was removed from the laptop. The lid was opened. The unlock screen appeared - but the place to type the password was not visible. The mouse cursor could be moved beyond the left edge of the screen, as if another screen was present. It appears the password field was being rendered on the other screen. Typing the password unlocked the laptop but it continued to think it was dual-headed. Closing and opening the lid again it started behaving normally.
