dash sometimes shown under the open windows

If I open the dash (or use the alt-tab switcher) it shows under the open windows many times, but I don't know what triggers this behavior. Once it happened to shown under one window, but above others..

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: unity 4.14.2-0ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-10.16-generic-pae 3.0.4
Uname: Linux 3.0.0-10-generic-pae i686
.tmp.unity.support.test.0:

ApportVersion: 1.22.1-0ubuntu2
Architecture: i386
CompizPlugins: [core,bailer,detection,composite,opengl,compiztoolbox,decor,imgpng,place,annotate,vpswitch,neg,gnomecompat,regex,grid,obs,resize,commands,move,mousepoll,unitymtgrabhandles,session,resizeinfo,animation,wall,workarounds,fade,expo,scale,ezoom,scaleaddon,unityshell]
CompositorRunning: compiz
Date: Sun Sep 11 09:47:02 2011
DistUpgraded: Fresh install
DistroCodename: oneiric
DistroVariant: ubuntu
DkmsStatus:
 bcmwl, 5.100.82.38+bdcom, 3.0.0-10-generic-pae, i686: installed
 tp-smapi, 0.41, 3.0.0-9-generic, i686: installed
 vboxhost, 4.1.2, 3.0.0-10-generic-pae, i686: installed
GraphicsCard:
 Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (primary) [8086:2a02] (rev 0c) (prog-if 00 [VGA controller])
   Subsystem: Lenovo T61 [17aa:20b5]
   Subsystem: Lenovo T61 [17aa:20b5]
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
MachineType: LENOVO 7661Z4R
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.0.0-10-generic-pae root=UUID=5a9d40dc-fc1a-43e7-b39b-a2fa66ef2581 ro quiet splash vt.handoff=7
SourcePackage: unity
UnitySupportTest: Error: command ['/usr/lib/nux/unity_support_test', '-p', '-f'] failed with exit code -11:
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/27/2007
dmi.bios.vendor: LENOVO
dmi.bios.version: 7LETA9WW (2.09 )
dmi.board.name: 7661Z4R
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr7LETA9WW(2.09):bd12/27/2007:svnLENOVO:pn7661Z4R:pvrThinkPadT61:rvnLENOVO:rn7661Z4R:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 7661Z4R
dmi.product.version: ThinkPad T61
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.5.92+bzr2791-0ubuntu2
version.libdrm2: libdrm2 2.4.26-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 7.11-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.11-0ubuntu3
version.xserver-xorg: xserver-xorg 1:7.6+7ubuntu7
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.0-1ubuntu13
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20110811.g93fc084-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.15.901-1ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110411+8378443-1