Users, which account information is obtained by ypbind from another machine, locking the terminal with klock are not able to unlock the terminal. Giving the correct password, klock says "failed". Users with a local account don't have this problem.
Please check your PAM settings (/etc/pam.d/kde) and version. Looks like a misconfiguration.
My PAM settings are (/etc/pam.d/kde) #%PAM-1.0 auth required /lib/security/pam_pwdb.so shadow nullok auth required /lib/security/pam_nologin.so account required /lib/security/pam_pwdb.so password required /lib/security/pam_cracklib.so password required /lib/security/pam_pwdb.so shadow nullok use_authtok session required /lib/security/pam_pwdb.so session optional /lib/security/pam_console.so My PAM version is pam-0.68-8
Should be fixed in the current version.