I'm -current as of this morning, the 28th. I upgraded from 13.1.
I'm using Xfce4, I've been using a button on my lower panel to launch xlock. Been working fine the last month. Upgraded to 13.37rc3.pi this morning.
Used my computer today for several hours today (after the upgrade). No problems. Hit my xlock launcher a couple hours ago, animation started. Turned monitor off. Then a few minutes ago, when I turned my monitor back on, black/blank screen, no password prompt. Killed xlock (had to use -s 9); no change. Saw xscreensaver was running, killed that too. No effect on my locked screen.
I then killed kdm and logged back in to an Xfce session. Back to normal now. I hit my xlock button. Got an animation up, typed in my password, and got back to my desktop no problem.
I'm not really sure what information to post to troubleshoot, but here's something for starters:
00:00.0 Host bridge: VIA Technologies, Inc. VT8366/A/7 [Apollo KT266/A/333]
00:01.0 PCI bridge: VIA Technologies, Inc. VT8366/A/7 [Apollo KT266/A/333 AGP]
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon RV100 QY [Radeon 7000/VE]