Strange artifacts in the login window background

[P. Selitskas]

I'm given strange graphic artefacts when the login window appears after Ubuntu starts. It started happening after updating to 12.04.

unity-greeter --test-mode also reproduces these artefacts so I made a screenshot.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xorg 1:7.6+12ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic-pae 3.2.14
Uname: Linux 3.2.0-24-generic-pae i686
.tmp.unity.support.test.0:

ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
CompizPlugins: [core,bailer,detection,composite,opengl,decor,mousepoll,vpswitch,regex,animation,snap,expo,move,compiztoolbox,place,grid,imgpng,gnomecompat,wall,ezoom,workarounds,resize,fade,unitymtgrabhandles,scale,session,unityshell]
CompositorRunning: compiz
Date: Wed May 23 17:35:21 2012
DistUpgraded: 2012-05-03 17:24:09,840 DEBUG failed to SystemUnLock() (E:Not locked)
DistroCodename: precise
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes, whatever it takes to get this fixed in Ubuntu
GraphicsCard:
 Intel Corporation 82G33/G31 Express Integrated Graphics Controller [8086:29c2] (rev 10) (prog-if 00 [VGA controller])
   Subsystem: Biostar Microtech Int'l Corp Device [1565:3103]
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
Lsusb:
 Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: BIOSTAR Group G31D-M7
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-24-generic-pae root=UUID=1e0f2655-11c1-40cd-a8d3-995756bf90f6 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to precise on 2012-05-03 (20 days ago)
dmi.bios.date: 06/05/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 080014
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: G31D-M7
dmi.board.vendor: BIOSTAR Group
dmi.chassis.asset.tag: None
dmi.chassis.type: 3
dmi.chassis.vendor: BIOSTAR Group
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr080014:bd06/05/2009:svnBIOSTARGroup:pnG31D-M7:pvr:rvnBIOSTARGroup:rnG31D-M7:rvr:cvnBIOSTARGroup:ct3:cvr:
dmi.product.name: G31D-M7
dmi.sys.vendor: BIOSTAR Group
version.compiz: compiz 1:0.9.7.8-0ubuntu1
version.libdrm2: libdrm2 2.4.32-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 8.0.2-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 8.0.2-0ubuntu3
version.xserver-xorg-core: xserver-xorg-core 2:1.11.4-0ubuntu10.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.7.0-0ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20111219.aacbd629-0ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.17.0-1ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1build2