Version: (using KDE Devel) Installed from: Compiled sources After locking the screen, it is not possible to unlock it by giving the user's password. The password is not accepted.
this isn't a plasma issue (not that you could know that, though =) and it's an installation issue. see http://techbase.kde.org/Getting_Started/Build/KDE4#Locked_sessions
*** Bug 152730 has been marked as a duplicate of this bug. ***
Just for the records the new link is http://techbase.kde.org/index.php?title=Getting_Started/Build/KDE4/Troubleshooting#Locked_sessions