SUMMARY
Double login is possible with the same user over the login GUI => but no double login, just two crapped logins - both unusable

STEPS TO REPRODUCE
- Start System (kubuntu 20.04 LTS - only one user available as set up during installation)
- Log in as user "user"
- Lock screen
- Choose "switch user"
- Screen switching seems to happen
- Log in now as "user" (again - no other user can be chosen here)
OBSERVED RESULT
 Log in seems to happen as for the first login, but no taskbar, autostart stuff
loads, when pressing Ctrl+Alt+F1 I get fractions of my previous login, but also
without taskbar, no real interaction with the GUI possible, etc. Pressing
Ctrl+Alt+F2 returns me to the "second" login, but this is still unusable.
- Way to get out: Either not using any gui until reboot (Ctrl+Alt+F3 => login,
sudo reboot) or sitting infinitely annoyed in front of two broken GUI logins...


EXPECTED RESULT
Either no login, because user is logged in already, return to the initial session or no second login possibility at all. At least a VERY BIG warning, that the system will become completely useless when proceeding would be helpful!

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: kubuntu 20.04 LTS (latest updates)

ADDITIONAL INFORMATION
Seems to be related to 103046 - but with the successor!