screen freezes occasionally when opening dash

[Oded Arbel]

With fully up to date vivid, sometimes when I open the dash the screen freezes. This usually happens when a 3D game is running.

System: Dell Latitude E5440 with Nvidia Optimus, running on the Intel integrated display (prime set to "intel").

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: compiz-core 1:0.9.12.0+15.04.20141219-0ubuntu1
ProcVersionSignature: Ubuntu 3.18.0-9.10-generic 3.18.2
Uname: Linux 3.18.0-9-generic x86_64
ApportVersion: 2.15.1-0ubuntu2
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CurrentDesktop: Unity
Date: Tue Jan 13 23:23:02 2015
DistUpgraded: Fresh install
DistroCodename: vivid
DistroVariant: ubuntu
ExecutablePath: /usr/bin/compiz
GraphicsCard:
 Intel Corporation Haswell-ULT Integrated Graphics Controller [8086:0a16] (rev 0b) (prog-if 00 [VGA controller])
   Subsystem: Dell Device [1028:05de]
InstallationDate: Installed on 2015-01-09 (3 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Alpha amd64 (20150109)
MachineType: Dell Inc. Latitude E5440
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.18.0-9-generic root=UUID=459f4711-4cd2-4fa9-a676-67ce56f74979 ro quiet splash vt.handoff=7
SourcePackage: compiz
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/01/2014
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A06
dmi.board.name: 08RCYC
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA06:bd05/01/2014:svnDellInc.:pnLatitudeE5440:pvr01:rvnDellInc.:rn08RCYC:rvrA00:cvnDellInc.:ct9:cvr:
dmi.product.name: Latitude E5440
dmi.product.version: 01
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.12.0+15.04.20141219-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.58-2
version.libgl1-mesa-dri: libgl1-mesa-dri 10.3.2-0ubuntu1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.3.2-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.16.2.901-1ubuntu3
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.0-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.4.0-2ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917-1~exp1ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu2
xserver.bootTime: Tue Jan 13 23:19:59 2015
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 8766
 vendor AUO
xserver.version: 2:1.16.2.901-1ubuntu3