momentary loss of connection to external monitor after screen turns off

I often use my laptop connected to an external monitor. After upgrade to 16.04 the following problem appears. Due to the discrepancy in workspace size, it causes all of my windows on my workspaces to get shuffled out of place and on wrong workspaces.

1. connect laptop to large screen (with different resolution than laptop screen).
2. turn laptop monitor off using the "Displays" configuration.
3. put windows on different workspaces.
4. let the machine sit until the screen turns off.
5. move the mouse.

6. see that the laptop screen flashes on before the monitor gets a signal.
7. this momentary switch from monitor to laptop and back to monitor puts the windows in disarray.

This is a regression. It's hard to work with mutiple windows as everything get shuffled.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity 7.4.0+16.04.20160415-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
NonfreeKernelModules: wl
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Tue May 3 09:04:22 2016
DistUpgraded: 2016-04-24 00:32:09,485 DEBUG icon theme changed, re-reading
DistroCodename: xenial
DistroVariant: ubuntu
DkmsStatus:
 bcmwl, 6.30.223.248+bdcom, 4.2.0-35-generic, x86_64: installed
 bcmwl, 6.30.223.248+bdcom, 4.4.0-21-generic, x86_64: installed
GraphicsCard:
 Intel Corporation Haswell-ULT Integrated Graphics Controller [8086:0a26] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Apple Inc. Haswell-ULT Integrated Graphics Controller [106b:011b]
InstallationDate: Installed on 2015-05-28 (340 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
MachineType: Apple Inc. MacBookAir6,2
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-21-generic.efi.signed root=UUID=88e88ee6-2dae-47e7-9ff1-dc2bc01a7112 ro noprompt persistent quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: Upgraded to xenial on 2016-04-23 (9 days ago)
dmi.bios.date: 10/26/2015
dmi.bios.vendor: Apple Inc.
dmi.bios.version: MBA61.88Z.0099.B21.1510261716
dmi.board.asset.tag: Base Board Asset Tag#
dmi.board.name: Mac-7DF21CB3ED6977E5
dmi.board.vendor: Apple Inc.
dmi.board.version: MacBookAir6,2
dmi.chassis.type: 10
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-7DF21CB3ED6977E5
dmi.modalias: dmi:bvnAppleInc.:bvrMBA61.88Z.0099.B21.1510261716:bd10/26/2015:svnAppleInc.:pnMacBookAir6,2:pvr1.0:rvnAppleInc.:rnMac-7DF21CB3ED6977E5:rvrMacBookAir6,2:cvnAppleInc.:ct10:cvrMac-7DF21CB3ED6977E5:
dmi.product.name: MacBookAir6,2
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.
version.compiz: compiz 1:0.9.12.2+16.04.20160415-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.2.0-1ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.2.0-1ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.18.3-1ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.1-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.7.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20160325-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Mon May 2 09:37:15 2016
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 41008
 vendor DEL
xserver.version: 2:1.18.3-1ubuntu2