"Displays" settings window went "missing" and there was no way to access it (though still open)

[teo1978]

I opened "System Settings" -> "Displays" (in order to restore my usual settings which had been reset because of bug 1671522).
I changed some settings (namely selected the laptop's built-in monitor and turned it off, leaving the external monitor turned on) and clicked Apply.
I'm not sure whether the issue (see below) happened at the stage or after the following:
I didn't click "keep current settings" in the popup, so the old settings were restored after 30 seconds (maybe I didn't see the popup because the issue had already happeded).

The issue is that now, even though the Display settings window was still open (I hadn't closed it, its icon was still in the Launcher, and the monitor identifier strings were displayed on the top-left corner of each monitor), it wasn't visible anywhere and I couldn't access it in any way.

Clicking on the window's icon on Launcher did not show the window and bring it to front. Hitting Alt+TAB and selecting the window would not show it. Hitting Ctrl+Super+D twice did nothing. Minimizing every other window did not reveal the window. There was just NO WAY of making the window visible and access it. I had to close it by right-clicking its laucher icon and selecting "quit", and then re-launch it.

Absolutely ridiculous. I'm pretty sure I have seen this happen other times randomly with other unrelated windows, usually (I think) with stuff like popups and the like (but now it seems it can happen with any kind of window, as in this case). It's not something that happens often, though.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity 7.4.0+16.04.20160906-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-64.85-generic 4.4.44
Uname: Linux 4.4.0-64-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
.proc.driver.nvidia.gpus.0000.01.00.0: Error: [Errno 21] Is a directory: '/proc/driver/nvidia/gpus/0000:01:00.0'
.proc.driver.nvidia.registry: Binary: ""
.proc.driver.nvidia.version:
 NVRM version: NVIDIA UNIX x86_64 Kernel Module 340.101 Thu Dec 1 15:52:31 PST 2016
 GCC version: gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4)
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
BootLog:
 [ OK ] Started LSB: Speech Dispatcher.
 [ OK ] Started LSB: Set the CPU Frequency Scaling governor to "ondemand".
 [ OK ] Started LSB: daemon to balance interrupts for SMP systems.
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: Thu Mar 9 16:32:26 2017
DistUpgraded: 2016-12-11 22:45:13,519 ERROR got error from PostInstallScript ./xorg_fix_proprietary.py (g-exec-error-quark: Failed to execute child process "./xorg_fix_proprietary.py" (No such file or directory) (8))
DistroCodename: xenial
DistroVariant: ubuntu
DpkgLog:

GraphicsCard:
 Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Acer Incorporated [ALI] 3rd Gen Core processor Graphics Controller [1025:0647]
 NVIDIA Corporation GF117M [GeForce 610M/710M/810M/820M / GT 620M/625M/630M/720M] [10de:1140] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: Acer Incorporated [ALI] GeForce 710M [1025:0691]
InstallationDate: Installed on 2013-10-11 (1244 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MachineType: Acer Aspire V3-571G
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-64-generic.efi.signed root=UUID=5830b30e-69e8-4bb4-8a2b-bc2b43c7414a ro quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: Upgraded to xenial on 2016-12-11 (87 days ago)
dmi.bios.date: 10/15/2012
dmi.bios.vendor: Acer
dmi.bios.version: V2.07
dmi.board.asset.tag: Type2 - Board Asset Tag
dmi.board.name: VA50_HC_CR
dmi.board.vendor: Acer
dmi.board.version: Type2 - Board Version
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: V2.07
dmi.modalias: dmi:bvnAcer:bvrV2.07:bd10/15/2012:svnAcer:pnAspireV3-571G:pvrV2.07:rvnAcer:rnVA50_HC_CR:rvrType2-BoardVersion:cvnAcer:ct10:cvrV2.07:
dmi.product.name: Aspire V3-571G
dmi.product.version: V2.07
dmi.sys.vendor: Acer
version.compiz: compiz 1:0.9.12.2+16.04.20160823-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.70-1~ubuntu16.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri 12.0.6-0ubuntu0.16.04.1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 12.0.6-0ubuntu0.16.04.1
version.nvidia-graphics-drivers: nvidia-graphics-drivers-* N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.18.4-0ubuntu0.2
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+git20160325-1ubuntu1.2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Thu Mar 9 16:21:28 2017
xserver.configfile: /etc/X11/xorg.conf
xserver.errors:
 NVIDIA(0): Failed to initiate mode change.
 NVIDIA(0): Failed to complete mode change
xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.18.4-0ubuntu0.2