Desktop canvas size stuck on screen resize

[jokerejoker]

I have a Dell XPS 13 9350 laptop with HiDPI screen.

I have the desktop scale set to 2 when using the builtin screen. When using an external monitor I have set the computer to move the desktop to the external monitor and set the desktop scale to 1.

This all work perfect except that the desktop background canvas does not seem be scaled along with the rest of the screen.

I have tried with the Dell D3100 DisplayLink dock and with the Dell WD15 dock. The issue does not seems to be related to the monitor/docking system, but the fact that the scaling is different between the screens.

Restart or logout>login fixes the problem, but this requires me to close all open programs, which is the reason for the inconvenience of the bug.

Having programs overlaying the desktop is not an issue, but when going back to the desktop the issue remains. Changing the background image does not affect the canvas size, but the image is changed for the area where the canvas was originally drawn.

I have attached an screen dump of the desktop after I attached the external monitor.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: unity-2d-shell (not installed)
Uname: Linux 4.6.0-040600rc3-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.19.1-0ubuntu5
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: Fri Apr 15 10:30:00 2016
DistUpgraded: Fresh install
DistroCodename: wily
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 5.0.14, 4.2.0-35-generic, x86_64: installed
 virtualbox, 5.0.14, 4.4.6-040406-generic, x86_64: installed
 virtualbox, 5.0.14, 4.5.0-040500-generic, x86_64: installed
EcryptfsInUse: Yes
GraphicsCard:
 Intel Corporation Sky Lake Integrated Graphics [8086:1916] (rev 07) (prog-if 00 [VGA controller])
   Subsystem: Dell Device [1028:0704]
InstallationDate: Installed on 2015-12-30 (106 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
MachineType: Dell Inc. XPS 13 9350
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.6.0-040600rc3-generic root=/dev/mapper/ubuntu--vg-root ro noprompt quiet splash vt.handoff=7
SourcePackage: unity
UdevLog: Error: [Errno 2] Ingen sådan fil eller filkatalog: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 03/01/2016
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.3.3
dmi.board.name: 0VM5NC
dmi.board.vendor: Dell Inc.
dmi.board.version: A01
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.3.3:bd03/01/2016:svnDellInc.:pnXPS139350:pvr:rvnDellInc.:rn0VM5NC:rvrA01:cvnDellInc.:ct9:cvr:
dmi.product.name: XPS 13 9350
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.12.2+15.10.20151202-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.64-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.0.2-1ubuntu4
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.0.2-1ubuntu4
version.xserver-xorg-core: xserver-xorg-core 2:1.17.2-1ubuntu9.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.2-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.5.0+git20150819-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20150808-0ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu3
xserver.bootTime: Fri Apr 15 08:30:51 2016
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 5194
 vendor SHP
xserver.version: 2:1.17.2-1ubuntu9.1