Description of problem: from time to time, kmix doesn't start and the lock / logout plasma applet doesn't work. It's nearly one time out of two that the problem appears. I can't logout using the logout plasma applet, but, if I open konsole, log as a root user and type 'shutdown now', the system turns off normally.
If I start kmix in a konsole terminal, kmix starts and no error messages are printed in the console.
*** This bug has been marked as a duplicate of bug 983110 ***