Desktop crashes and login window appears

[venoel]

It happens randomly

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xorg 1:7.7+1ubuntu8.1
ProcVersionSignature: Ubuntu 3.19.0-31.36~14.04.1-generic 3.19.8-ckt7
Uname: Linux 3.19.0-31-generic i686
.tmp.unity.support.test.0:

ApportVersion: 2.14.1-0ubuntu3.18
Architecture: i386
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
Date: Mon Nov 2 16:09:54 2015
DistUpgraded: Fresh install
DistroCodename: trusty
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Hewlett-Packard Company Device [103c:183e]
 Advanced Micro Devices, Inc. [AMD/ATI] Thames [Radeon HD 7500M/7600M Series] [1002:6840] (rev ff) (prog-if ff)
InstallationDate: Installed on 2015-10-20 (13 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta i386 (20150805)
MachineType: Hewlett-Packard HP Pavilion g6 Notebook PC
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.19.0-31-generic root=UUID=bd55f751-d5aa-4354-8ce8-a12402a8c4b3 ro
SourcePackage: xorg
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 11/01/2012
dmi.bios.vendor: Insyde
dmi.bios.version: F.17
dmi.board.asset.tag: Type2 - Board Asset Tag
dmi.board.name: 183E
dmi.board.vendor: Hewlett-Packard
dmi.board.version: 56.2D
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnInsyde:bvrF.17:bd11/01/2012:svnHewlett-Packard:pnHPPaviliong6NotebookPC:pvr0889110000085910000600000:rvnHewlett-Packard:rn183E:rvr56.2D:cvnHewlett-Packard:ct10:cvrChassisVersion:
dmi.product.name: HP Pavilion g6 Notebook PC
dmi.product.version: 0889110000085910000600000
dmi.sys.vendor: Hewlett-Packard
version.compiz: compiz 1:0.9.11.3+14.04.20150313-0ubuntu1
version.libdrm2: libdrm2 2.4.60-2~ubuntu14.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri N/A
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.xserver-xorg-core: xserver-xorg-core N/A
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel N/A
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau N/A
xserver.bootTime: Mon Nov 2 15:56:41 2015
xserver.configfile: default
xserver.errors: RADEON(G0): [XvMC] Failed to initialize extension.
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 900
 vendor LGD
xserver.version: 2:1.17.1-0ubuntu3~trusty1

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.