Window moved to another monitor after coming back from screen lock

[Hoon Choi]

Steps to reproduce:

1. Open an application (tested Firefox and LibreOffice Writer; same behaviour is observed with both) on desktop with two monitors.
2. Open another window of the same application (by pressing Ctrl+N).
3. Move the new window to the other monitor so that each monitor has a window open.
4. Maximize both windows.
5. Open another application (tested Terminal). Keep the focus on this application.
6. Wait until the screen goes to sleep and locks due to inactivity (the default is 5 minutes).
7. Unlock the screen by entering password.
8. One of the maximized windows is moved to the other monitor, so one monitor has both windows.

Affected machine configuration:

- AMD Radeon R9 280X (w/ 'radeon' driver)
- 1920x1200 screen (monitor 1) and 1920x1080 screen (monitor 2) connected to the Radeon R9 280X
 - monitor 2 is set to the left of monitor 1 in System Settings
- Ubuntu 16.04 fresh install with updates applied
- Intel Core i5-3570K

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity 7.4.0+16.04.20160526.1-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-24.43-generic 4.4.10
Uname: Linux 4.4.0-24-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2.1
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: Mon Jun 20 21:07:15 2016
DistUpgraded: Fresh install
DistroCodename: xenial
DistroVariant: ubuntu
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Tahiti XT [Radeon HD 7970/8970 OEM / R9 280X] [1002:6798] (prog-if 00 [VGA controller])
   Subsystem: Micro-Star International Co., Ltd. [MSI] Tahiti XT [Radeon HD 7970/8970 OEM / R9 280X] [1462:2775]
GsettingsChanges:
 b'org.compiz.core' b'outputs' b"['1920x1200+1920+0', '1920x1080+0+0']"
 b'org.compiz.core' b'active-plugins' b"['core', 'composite', 'opengl', 'compiztoolbox', 'resize', 'grid', 'move', 'wall', 'place', 'session', 'copytex', 'mousepoll', 'imgpng', 'commands', 'vpswitch', 'snap', 'regex', 'unitymtgrabhandles', 'animation', 'workarounds', 'fade', 'expo', 'scale', 'ezoom', 'unityshell']"
 b'com.ubuntu.user-interface' b'scale-factor' b"{'DVI-0': 8, 'DisplayPort-0': 8}"
 b'org.gnome.desktop.interface' b'gtk-im-module' b"'gtk-im-context-simple'"
 b'org.gnome.desktop.interface' b'scaling-factor' b'uint32 1'
InstallationDate: Installed on 2016-06-20 (0 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
MachineType: Gigabyte Technology Co., Ltd. To be filled by O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-24-generic root=UUID=9f245075-0a78-422f-9095-d4ead345a438 ro quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/24/2012
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: F18
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: Z77X-UD3H
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: To be filled by O.E.M.
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrF18:bd10/24/2012:svnGigabyteTechnologyCo.,Ltd.:pnTobefilledbyO.E.M.:pvrTobefilledbyO.E.M.:rvnGigabyteTechnologyCo.,Ltd.:rnZ77X-UD3H:rvrTobefilledbyO.E.M.:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To be filled by O.E.M.
dmi.product.version: To be filled by O.E.M.
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
version.compiz: compiz 1:0.9.12.2+16.04.20160526-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1ubuntu0.16.04.1
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 2:1.18.3-1ubuntu2.2
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 Jun 20 19:49:48 2016
xserver.configfile: default
xserver.devices:
 input Power Button KEYBOARD, id 6
 input Power Button KEYBOARD, id 7
 input USB Keyboard KEYBOARD, id 8
 input USB Keyboard KEYBOARD, id 9
 input Logitech USB-PS/2 Optical Mouse MOUSE, id 10
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.18.3-1ubuntu2.2
xserver.video_driver: radeon

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.