I am using Leap 42.1, upgraded from openSuSE 13.2. 
I locked the screen manually on Dec 18, 2015 and left for 2 weeks of vacation.
When I tried to unlock the screen today (Jan 4, 2016), it failed with "invalid
password" (or something similiar, can't remember the exact text). 
I logged in into the console using the same account and password, which worked
OK.
I then switched to root and killed (-9) the kscreenlocker_greet process, which
restarted the screen locker (after some seconds). On this new instance of the
screen locker, I could successfully login using the same credentials as in the
beginning.
Checking "kcheckpass" showed no problem, it did evaluate the password for the
account correctly.
Manually locking the screen and unlocking it again showed no problem.