When using the systemd command 'systemctl suspend' in order to suspend to RAM there is no password prompt when resuming from sleep. The computer goes straight to the desktop. IIRC the same is true with 'systemctl hibernate' but I can't really test right now as hibernation is not functional. When using the usual suspend button from Kickoff the password prompt is shown. Reproducible: Always
Also happens with Opensuse 12.3 KDE4.11.4. I did not wait very long between 'systemctl suspend' and pressing power button to resume, so I don't know if this is a time dependent thing or not.
it is arguable that the login manager should also take care of screen locking, but as this is not the case in the classical kdm/kscreenlocker configuration, this belongs to the screen locker.
implemented in 5.2