Trying to lock my screen via the "lock" button will not actually give me the login screen necessary to unlock it again. The same thing happens if I send my laptop to sleep, there's no place to log in at wake up, only the touchpad icon greets me. The solution in both cases is: send laptop to sleep (again). On wake up, I can log in.
I'm greeted with a "screenshot" of my workspace that I can't interact with, except for the side bar still reacting with showing icons and displaying their names on hovering upon them. I can even start applications, but won't be able to actually interact until after logging in.
(I've posted in the newbie area with no success 5 days ago.)