Just moving the lock up a notch would "fix" it, but the primary issue is that the lock screen should not be a layer in the shell, but its own lock "window", so it sits above the panel and cannot be covered by it. The issue is a bit bigger than thought at first.

jep, since the panel is now a window the lock screen can't cover it anymore.
that should be done in its own process or even in kwin, but volunteers needed for that ;)

how about not displaying the applauncher-strip/panel at all in this situation? I mean, its not clickable anyway, if the intention is to unlock the screen. 

So simply showing for example a clock and the locking symbol is sufficient, in my opinion.

But all that comment simply from a UID point of view, I Dont know the technical feasability...

yep, that is what should be done: showing only the unlock screen (that could have simply a clock or whatever) and nothing else.

however, we are keeping it in this undefined state because technically it has to be done differently, in another process with the window manager ensuring that no other window can go over it, that is kinda a different problem. there was someone volunteering to do it so let's see

well, two things probably should be done:

* the window manager should be aware of the lock window so it can suspend compositing of other windows, etc.

* the lock screen be put in its own window, and this window registered as a "lock window" which would make it full screen, etc. via the window manager.

iow, handle it very much like we do the dashboard now with kwin.

Just strikes me that an app can suspend compositing already, so probably kwin doesn't need to be aware of that (for this reason, at least).

The unlock symbol is now placed at another position, thus this bug applicable any more and can also be closed

Lock screen layout has been fixed.