After timeout the KDE screensaver kicks in showing login dialog, exactly the
same as when the screen is locked (user name, password, etc). Despite that the
screen is not locked at all, pressing any key gets rid of the saver screen.

This could be a security threat, tricking users to think they are safe while
that's not the case.

This is a security-issue bug that was raised by the security team within openSUSE.  I agree with this statement as that with the current layout of the simple screenlocker one get indeed the feeling that the screen is locked as that the password dialog box is on the screen.  The password dialog and the statement that the screen is locked, should only appear if the screen is actually locked !!

Reproducible: Always