light-locker switches disabled screen on (when used with xfce)

[Viktor Pal]

So what happens is light-locker switches the screen that was disabled in xfce on and leaves it on after login.

To reproduce:
Desktop environment is Xfce (Xubuntu) with lightdm and light-locker.

1.) Attach an external display to a laptop and configure the DE to only use external display. Laptop display will be powered off and only the external display will be on.
2.) Now lock your screen using the Whisker Menu or wait until the xfce4-power-manager locks it. Now both screens are powered off.
3.) Try to log in (hit any key on the keyboard or move the mouse). Now both displays are switched on and the login prompt is displayed on both of the (with the resolution of the bigger so looks strange on the built in display).
4.) After you are logged in the built in display that was powered off before locking the screen is on (it does not display anything as it was disabled in xfce). It is blank (black) but you can see that the backlight is on.

I'm not sure if light-locker shouldn't switch on the disabled screen and respect DE display configuration or if xfce4-power-manager should take care of shutting down the disabled display again after login.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: light-locker (not installed)
ProcVersionSignature: Ubuntu 4.2.0-18.22-generic 4.2.3
Uname: Linux 4.2.0-18-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: GNOME
Date: Sun Nov 29 19:30:01 2015
SourcePackage: light-locker
UpgradeStatus: Upgraded to wily on 2015-10-22 (37 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[intherye (intherye)]

I'm seeing this problem also on Xubuntu 16.04.1

I can also add another symptom to the reporters observations:

5) When locking the screen again with Ctrl+Alt+Del both screens are blanked (background light still on) and the computer does not react to keyboard inputs (I can SSH in).

[intherye (intherye)]

I want to add that this problem occurred since upgrading from Trusty to Xenial. I'ver never seen it in Trusty.

[Péter (xfaeznimltegstg)]

I made a quick test in my recent Xubuntu (16.10, light-locker-command 1.7.0).

$ light-locker-command -V
light-locker-command 1.7.0

$ light-locker-command --lock

Both monitors switches off, as they should be.
(A waited a bit, though not very much.)
When resuming, after typing the password, the "unused" monitor goes back to off (backlight off too) state, as it should be.

Similar results for suspending.
So the bug does not seem to appear.

[Theo Linkspfeifer (lastonestanding)]

Did anyone of you test with Xubuntu 18.04 yet?

[Launchpad Janitor (janitor)]

[Expired for light-locker (Ubuntu) because there has been no activity for 60 days.]