alt tab crashes with radeon graphics

Binary package hint: unity

this is not the same as https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/684745
Alt-tabbing causes compiz to crash.
The error messages given are different from the previous bug.

$ tail -n 1 .xsession
drmRadeonCmdBuffer: -22. Kernel failed to parse or rejected command stream. See dmesg for more info.

$ dmesg | tail -n 3
[ 236.991525] radeon 0000:01:05.0: r600_cs_track_check:361 mask 0x0000000F | 0x0000000F no cb for 0
[ 236.991536] radeon 0000:01:05.0: r600_packet3_check:1330 invalid cmd stream 502
[ 236.991543] [drm:radeon_cs_ioctl] *ERROR* Invalid command stream !

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: unity 3.4.0-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-1.28-generic 2.6.38-rc2
Uname: Linux 2.6.38-1-generic x86_64
NonfreeKernelModules: wl
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/allscreens/options/active_plugins'
CompositorRunning: compiz
DRM.card0.DP.1:
 status: disconnected
 enabled: disabled
 dpms: On
 modes:
 edid-base64:
DRM.card0.HDMI.A.1:
 status: disconnected
 enabled: disabled
 dpms: On
 modes:
 edid-base64:
DRM.card0.LVDS.1:
 status: connected
 enabled: enabled
 dpms: On
 modes: 1366x768 1280x720 1152x768 1024x768 800x600 848x480 720x480 640x480
 edid-base64: AP///////wAGrywwAAAAAAAUAQSQHRB4AhWFl1hTiiYlUFQAAAABAQEBAQEBAQEBAQEBAQEBSh1WxFAAIDAwIDYAJaQQAAAaSh1WxFAAIDAwIDYAJaQQAAAaAAAA/gAzMDFGNIBCMTMzWFczAAAAAAAAQQKWAREAAAEBCiAgAI4=
Date: Mon Jan 31 22:46:15 2011
DistUpgraded: Yes, recently upgraded Log time: 2011-01-23 22:53:25.334151
DistroCodename: natty
DistroVariant: ubuntu
DkmsStatus:
 bcmwl, 5.100.82.38+bdcom, 2.6.38-1-generic, x86_64: installed
 bcmwl, 5.100.82.38+bdcom, 2.6.37-12-generic, x86_64: installed
GraphicsCard: Subsystem: Dell Device [1028:044b]
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20101202)
InstallationMedia_: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20101202)
MachineType: Dell Inc. Inspiron M301Z
ProcEnviron:
 LANGUAGE=en_GB.UTF-8:en
 LANG=en_GB.UTF-8
 LC_MESSAGES=en_AG.utf8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-1-generic root=UUID=539f27a4-85c4-419d-a3f7-1195332b6970 ro quiet splash vt.handoff=7
ProcVersionSignature_: Ubuntu 2.6.38-1.28-generic 2.6.38-rc2
Renderer: Hardware acceleration
SourcePackage: unity
UnitySupportTest:

dmi.bios.date: 07/16/2010
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A03
dmi.board.vendor: Dell Inc.
dmi.board.version: A03
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: A03
dmi.modalias: dmi:bvnDellInc.:bvrA03:bd07/16/2010:svnDellInc.:pnInspironM301Z:pvrA03:rvnDellInc.:rn:rvrA03:cvnDellInc.:ct8:cvrA03:
dmi.product.name: Inspiron M301Z
dmi.product.version: A03
dmi.sys.vendor: Dell Inc.
version.libdrm2: libdrm2 2.4.23-1ubuntu3
version.libgl1-mesa-glx: libgl1-mesa-glx 7.10-1ubuntu1
version.xserver-xorg: xserver-xorg 1:7.5+6ubuntu8
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.13.2+git20110124.fadee040-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.14.0-1ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110107+b795ca6e-0ubuntu1