Dual head system - black background on second screen

[Colin Law]

On up to date Xenial beta, on a dual screen system, sometimes on boot (maybe one in three times) the second monitor shows a black background instead of the wallpaper.

The first monitor (the laptop screen) shows the wallpaper correctly. If I go to System Settings > Appearance and change the mode from Zoom to Scale it is shown on both screens, changing it back to Zoom again keeps the wallpaper on both screens. Apart from the missing wallpaper the display operates as normal.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity 7.4.0+16.04.20160322-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-15.31-generic 4.4.6
Uname: Linux 4.4.0-15-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,vpswitch,snap,mousepoll,resize,place,move,wall,grid,regex,imgpng,session,gnomecompat,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Sat Mar 26 08:08:37 2016
DistUpgraded: 2016-03-06 15:14:34,184 DEBUG enabling apt cron job
DistroCodename: xenial
DistroVariant: ubuntu
GraphicsCard:
 Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: Fujitsu Limited. 4th Gen Core Processor Integrated Graphics Controller [10cf:17a9]
InstallationDate: Installed on 2014-10-21 (521 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20141017)
MachineType: FUJITSU LIFEBOOK A544
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-15-generic root=UUID=c68c6484-d8d6-44f6-b429-892aa6ef74cf ro
SourcePackage: unity
UpgradeStatus: Upgraded to xenial on 2016-03-06 (19 days ago)
dmi.bios.date: 10/05/2015
dmi.bios.vendor: FUJITSU // Phoenix Technologies Ltd.
dmi.bios.version: Version 1.20
dmi.board.name: FJNBB35
dmi.board.vendor: FUJITSU
dmi.chassis.type: 10
dmi.chassis.vendor: FUJITSU
dmi.modalias: dmi:bvnFUJITSU//PhoenixTechnologiesLtd.:bvrVersion1.20:bd10/05/2015:svnFUJITSU:pnLIFEBOOKA544:pvr:rvnFUJITSU:rnFJNBB35:rvr:cvnFUJITSU:ct10:cvr:
dmi.product.name: LIFEBOOK A544
dmi.sys.vendor: FUJITSU
upstart.unity7.log: ReminderFox clh(1) {rmFx_cmdLine: [xpconnect wrapped nsICommandLine]}
version.compiz: compiz 1:0.9.12.2+16.04.20160318-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.1.2-1ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.1.2-1ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.18.1-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.1-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.6.1-1ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20160218-1ubuntu3
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Sat Mar 26 07:49:43 2016
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 13890
 vendor SEC
xserver.version: 2:1.18.1-1ubuntu4