I think I've reproduced this same error, though the scenario is slightly different:

System Info
- Lenovo thinkpad X200 notebook
-  Intel GM45 Express graphics
- Ubuntu 12.04 32bit (x86-32).  up-to-date as of June 2 / 2012

Steps to reproduce
- set setting "when the lid is closed"="do nothing" in Power settings
- set "Lock" to "On" in Brightness and Lock settings
- check "Require my password when waking from suspend" in Brightness and Lock settings
- close the lid
- open the lid

expected results:  I see the log in dialog

actual result:  backlit but dark screen, mouse cursor still moves as normal, mouse cursor changes  as I move it around the screen as if it is responding to diff't UI elements.  Occasionally the display is different:  instead of blank/black screen other windows are visible, such as the dock and the top panel... but when that happens I cannot interact with them.

The issue is intermittent.  Cannot be reproduced all the time.

Snippet from Xorg.0.log:
[204557.220] (II) intel(0): EDID vendor "LEN", prod id 16401
[204557.220] (II) intel(0): Printing DDC gathered Modelines:
[204557.220] (II) intel(0): Modeline "1280x800"x0.0   69.30  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (49.2 kHz)
[204557.220] (II) intel(0): Modeline "1280x800"x0.0   57.79  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (41.0 kHz)
[204558.022] (WW) intel(0): flip queue failed: Invalid argument
[204558.022] (WW) intel(0): Page flip failed: Invalid argument
[204568.948] (II) intel(0): EDID vendor "LEN", prod id 16401
[204568.948] (II) intel(0): Printing DDC gathered Modelines:
[204568.948] (II) intel(0): Modeline "1280x800"x0.0   69.30  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (49.2 kHz)
[204568.948] (II) intel(0): Modeline "1280x800"x0.0   57.79  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (41.0 kHz)
[204569.789] (II) intel(0): Allocated new frame buffer 1920x1080 stride 7680, tiled
[204599.362] (II) PM Event received: Capability Changed
[204599.362] I830PMEvent: Capability change
[232228.461] (II) intel(0): EDID vendor "LEN", prod id 16401
[232228.461] (II) intel(0): Printing DDC gathered Modelines:
[232228.461] (II) intel(0): Modeline "1280x800"x0.0   69.30  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (49.2 kHz)
[232228.461] (II) intel(0): Modeline "1280x800"x0.0   57.79  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (41.0 kHz)
[232229.278] (II) intel(0): Allocated new frame buffer 1280x800 stride 5120, tiled
[232235.012] (II) PM Event received: Capability Changed
[232235.012] I830PMEvent: Capability change
[232240.008] (II) PM Event received: Capability Changed
[232240.009] I830PMEvent: Capability change
[232240.092] (II) intel(0): EDID vendor "LEN", prod id 16401
[232240.093] (II) intel(0): Printing DDC gathered Modelines:
[232240.093] (II) intel(0): Modeline "1280x800"x0.0   69.30  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (49.2 kHz)
[232240.093] (II) intel(0): Modeline "1280x800"x0.0   57.79  1280 1304 1336 1408  800 804 808 820 +hsync +vsync (41.0 kHz)
[232267.256] (II) AIGLX: Suspending AIGLX clients for VT switch

Gut feeling:  the windows that are supposed to be drawn when the computer is locked eg:  when just the wallpaper and the login dialog are supposed to be visible) are for some reason not rendered at the front, though they are the 'active' windows (I'm not an X programmer so I'm not sure of the right X terminology).

I don't recall this being an issue on either of 11.04 or 11.10.