screen darkening does not work correctly on high-dpi screen

[Andreas E.]

When "Control Center → Brightness and Lock → Darken the screen to save energy" is set, the screen fades slowly into black after a certain time of inactivity. On a high-dpi screen, it fades only the upper left quarter of the screen and keeps the rest visible.

The same is the case when a password is required or before and after stand-by, that means a view of the personal desktop is partly (3/4) exposed even before the owner types the password. (Apart from that it looks embarrassing.)

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: unity 7.3.1+14.10.20141016-0ubuntu1
Uname: Linux 3.18.0-031800-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
BootLog:
 URfkill[517]: Starting urfkilld version 0.6.0

  * Setting up X socket directories... 
[ OK ]
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: Sat Dec 27 11:09:30 2014
DistUpgraded: 2014-11-04 18:35:56,188 DEBUG enabling apt cron job
DistroCodename: utopic
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 4.3.18, 3.16.0-25-generic, x86_64: installed
 virtualbox, 4.3.18, 3.16.0-28-generic, x86_64: installed
 virtualbox, 4.3.18, 3.18.0-031800-generic, x86_64: installed
EcryptfsInUse: Yes
GraphicsCard:
 Intel Corporation Haswell-ULT Integrated Graphics Controller [8086:0a16] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:3978]
InstallationDate: Installed on 2014-02-02 (327 days ago)
InstallationMedia: Ubuntu-GNOME 14.04 "Trusty Tahr" - Alpha amd64 (20140201)
MachineType: LENOVO 20266
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.18.0-031800-generic root=UUID=4bfb3686-b9f7-487d-81f6-eceb41097ad9 ro quiet splash acpi_backlight=vendor vt.handoff=7
SourcePackage: unity
UpgradeStatus: Upgraded to utopic on 2014-11-04 (52 days ago)
dmi.bios.date: 10/31/2013
dmi.bios.vendor: LENOVO
dmi.bios.version: 76CN31WW
dmi.board.asset.tag: No Asset Tag
dmi.board.name: Yoga2
dmi.board.vendor: LENOVO
dmi.board.version: 31900058STD
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo Yoga 2 Pro
dmi.modalias: dmi:bvnLENOVO:bvr76CN31WW:bd10/31/2013:svnLENOVO:pn20266:pvrLenovoYoga2Pro:rvnLENOVO:rnYoga2:rvr31900058STD:cvnLENOVO:ct10:cvrLenovoYoga2Pro:
dmi.product.name: 20266
dmi.product.version: Lenovo Yoga 2 Pro
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.12+14.10.20140918-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.56-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.3.0-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.3.0-0ubuntu3
version.xserver-xorg-core: xserver-xorg-core 2:1.16.0-1ubuntu1.2
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 2:2.99.914-1~exp1ubuntu4.1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu2
xserver.bootTime: Fri Dec 26 19:39:15 2014
xserver.configfile: /etc/X11/xorg.conf
xserver.errors: [dix] ELAN Touchscreen: unable to find touch point 0
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 16970
 vendor SDC
xserver.version: 2:1.16.0-1ubuntu1.2