Broken users session management

[Germano Massullo]

By several months, the entire management of multiple users sessions is
broken.
In past I used sometimes to leave my machine to another person, so I
locked my user session, and started another user "foo" session. Then
when user foo finished to use my machine, he ended his session, so I
unlocked mine and continued to work normally.

Now such actions are no longer possible in Plasma 5 because for unknown
reasons, the locked user session will be killed as soon you start
another user session.

Any feedbacks about?