Focused window not visible

[Teo]

The screenshot shows a situation that shouldn't ever be possible under any circumstances:
The currently focused window, which should be on the foreground, is invisible.

I have several applications open and I switched from one to another several times. Among them is one Nautilus window. Now, I click on the Nautilus icon in the Launcher, and the Nautilus window which gets focus does not appear anywhere. You can tell that every other window looses focus, and you can see that the Launcher icon has the triangle on the right indicating the Nautilus window has focus. Also, the menu on the top of the screen is Nautilus's.

No matter how many times I try to switch window, no matter if I show and hide desktop, there's no way I get to see that window.

There's NO EASY WAY TO REPRODUCE THAT I KNOW OF (hence please don't tell me "can't reproduce", I don't expect you to be able to). It just happened.

I guess this is extremely rare. I seem to remember this is not the very first time I see this happen, but it might well be just the second. In my whole life.
Still a bug.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: unity 7.3.3+15.10.20151203-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-27.32-generic 4.2.8-ckt1
Uname: Linux 4.2.0-27-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CurrentDesktop: Unity
Date: Fri Feb 19 12:59:07 2016
InstallationDate: Installed on 2013-10-11 (860 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
SourcePackage: unity
UpgradeStatus: Upgraded to wily on 2016-01-18 (32 days ago)