I can't use the "leave" buttons as they don't do anything. The two buttons I've tried are in the right click menu on the desktop-background, and the other is in the KDE menu (which gives you many options such as sleep, hibernate, etc) -- the logout, reboot and poweroff options don't work (the switch user does work, and the others I haven't tried).

I especially like using the right click option, but it hasn't been working for at least the last two versions of KDE. The only way that I can reboot or poweroff is by using a terminal. How do I fix this? Or is this a bug?

Can you reproduce under a new user?