Forwarding this bug from Ubuntu reporter Martin Pool:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/752157

[Problem]
On RS880 solid grey rectangles appear over icon text and window borders in some applications in a compositing environment, namely Unity's launcher.  Unity developers are able to reproduce this and say it is a video driver / mesa issue.

[Original Description]
on current natty, clicking the Ubuntu button in the top left shows a window with graphical corruption as shown in the attached screenshot.  sometimes there are solid grey rectangles over the icon text too.

DistroRelease: Ubuntu 11.04
Package: unity 3.8.2-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-8.41-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
Architecture: amd64
CompizPlugins: [core,bailer,detection,composite,opengl,decor,mousepoll,vpswitch,regex,animation,snap,expo,move,compiztoolbox,place,gnomecompat,wall,ezoom,workarounds,staticswitcher,resize,fade,scale,session,unityshell]
CompositorRunning: compiz
DRM.card0.DVI.D.1:
 status: connected
 enabled: enabled
 dpms: On
 modes: 1920x1200 1600x1200 1680x1050 1280x1024 1280x1024 1152x864 1024x768 1024x768 800x600 800x600 640x480 640x480 720x400
 edid-base64: AP///////wAQrDCgUzE0MBMTAQOAOiR46un1rFEwtCURUFSlSwCBgKlAcU+zAAEBAQEBAQEBKDyAoHCwI0AwIDYARmwhAAAaAAAA/wBSSzUxNDk1ODA0MVMKAAAA/ABERUxMIDI3MDlXCiAgAAAA/QA4TB5TEQAKICAgICAgAHU=
DRM.card0.VGA.1:
 status: disconnected
 enabled: disabled
 dpms: On
 modes: 
 edid-base64:
Date: Wed Apr  6 13:21:21 2011
DistUpgraded: Log time: 2010-12-21 12:35:39.044742
DistroCodename: natty
DistroVariant: ubuntu
EcryptfsInUse: Yes
GraphicsCard:
 ATI Technologies Inc RS880 [Radeon HD 4290] [1002:9714] (prog-if 00 [VGA controller])
   Subsystem: Giga-byte Technology Device [1458:d000]
MachineType: Gigabyte Technology Co., Ltd. GA-890GPA-UD3H
ProcEnviron:
 LANGUAGE=en_AU:en
 PATH=(custom, user)
 LANG=en_AU.UTF-8
 SHELL=/bin/zsh
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-2.6.38-8-generic root=/dev/mapper/vg_main-natty_64 ro clock=hpet quiet splash rootdelay=10 vt.handoff=7
ProcVersionSignature_: Ubuntu 2.6.38-8.41-generic 2.6.38.2
ProcVersionSignature__: Ubuntu 2.6.38-8.41-generic 2.6.38.2
Renderer: Unknown
SourcePackage: unity
UpgradeStatus: Upgraded to natty on 2010-12-21 (105 days ago)
XorgConf:
 Section "Device"
 	Identifier	"Configured Video Device"
 	Option	"SWCursor"	"on"
 EndSection
dmi.bios.date: 05/04/2010
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: F7c
dmi.board.name: GA-890GPA-UD3H
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF7c:bd05/04/2010:svnGigabyteTechnologyCo.,Ltd.:pnGA-890GPA-UD3H:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-890GPA-UD3H:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: GA-890GPA-UD3H
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
version.compiz: compiz 1:0.9.4git20110322-0ubuntu5
version.ia32-libs: ia32-libs 20090808ubuntu11
version.libdrm2: libdrm2 2.4.23-1ubuntu6
version.libgl1-mesa-dri: libgl1-mesa-dri 7.10.1-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.10.1-0ubuntu3
version.xserver-xorg: xserver-xorg 1:7.6+4ubuntu3
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.0-0ubuntu4
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.14.0-4ubuntu6
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110107+b795ca6e-0ubuntu6