Forwarding this bug from Ubuntu reporter Emmanuel Pacaud:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/542533

[Problem]
When shifting to another workspace, the screen clears to black for a moment before transitioning to the other workspace.

[Original Description]
I have desktop effects enabled, using "Desktop wall" for workspace transitions.

When I select another workspace, the desktop goes black during the transition, only showing the workspace overview OSD.

It also goes black during the transition if the "Cube" effect is selected.

There's no broken screen state in this issue. The screen goes mostly black, except for the panel and the workspace switching OSD, only during the workspace transition. After the transisition, everything works fine.

Architecture: i386
Date: Sat Mar 20 10:13:18 2010
DistroRelease: Ubuntu 10.04
DkmsStatus: Error: [Errno 2] Aucun fichier ou dossier de ce type
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Alpha i386 (20100119)
MachineType: System Manufacturer System Name
Package: xorg 1:7.5+3ubuntu1
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.32-16-generic root=UUID=cad49b82-547e-477f-a13d-c5f825c88e3c ro quiet splash
ProcEnviron:
 LANG=fr_FR.utf8ProcVersionSignature: Ubuntu 2.6.32-16.25-generic
SourcePackage: xorg
Symptom: display
Uname: Linux 2.6.32-16-generic i686
dmi.bios.date: 09/02/2004
dmi.bios.vendor: Award Software, Inc.
dmi.bios.version: ASUS A7V8X-X ACPI BIOS Revision 1013
dmi.board.name: A7V8X-X
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: REV 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 7
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAwardSoftware,Inc.:bvrASUSA7V8X-XACPIBIOSRevision1013:bd09/02/2004:svnSystemManufacturer:pnSystemName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnA7V8X-X:rvrREV1.xx:cvnChassisManufacture:ct7:cvrChassisVersion:
dmi.product.name: System Name
dmi.product.version: System Version
dmi.sys.vendor: System Manufacturer
glxinfo: Error: [Errno 2] Aucun fichier ou dossier de ce type
system: codename:           lucid
 architecture:       i686
 kernel:             2.6.32-16-generic

[lspci]
01:00.0 VGA compatible controller [0300]: ATI Technologies Inc RV280 [Radeon 9200] [1002:5961] (rev 01)
    	Subsystem: ASUSTeK Computer Inc. Device [1043:5002]