On several freshly installed systems with KDE, the screen saver won't lock the
screen while a different virtual terminal is active.

I can see the Problem with opensuse-Leap-15.1 as well as with ubuntu-18.04
(when kubuntu-desktop is installed)

How to reproduce:

1. Configure the screen saver to 1 minute and require the password after
additional 5 seconds.

2. While the screen saver in not active, activate a different virtual terminal
(e.g. by pressing CTL-ALT-F2)

3. Wait for more than 70 seconds.

4. Switch back to the desktop

Expected behavior: Screen saver is active and only the password screen is
visible.

Actual behavior: when switching back, all the open applications (possibly
showing confidential data!) are visible for about one second. Only then the
screen starts to dim. And due to the setting of 5 seconds for password
requirement,
one can stop the screen saver just by typing some key or moving the mouse.

Result of mailing list discussion so far:
- Problem can be reproduced by other people
- Problem does appear with sddm, lightdm and kdm
- Problem does not seem to appear with gdm and xfce

Mailing list thread: https://lists.opensuse.org/opensuse/2020-03/msg00267.html