Ghost window & launcher icon not selected when opening a folder in external disk

[teo1978]

I have an external disk connected via USB; it contains several logical units one of which is called "IOM_data".

Steps to reproduce the issue:

1. Open Nautilus
2. On the left panel, select the IOM_data unit

Expected behavior:
Should display the contents of the external disk unit, and Nautilu's Launcher icon should still be selected.

Observed behavior:
Displays the contents of the external unit, but the Launcher icon of Nautilus is no longer highlighted, not only that, it doesn't have any triangle on the left of it, as if no Nautilus window was open at all.

Additional steps:
3. Now click on Nautilus' Launcher icon

Expected result:
Since the icon should be already selected in the first place, nothing should happen at all. If in the meantime you had given focus to some other window, this should simply give focus back to the existing Nautilus window where you had opened the external disk unit.

Observed result:
This opens a NEW Nautilus window, showing by default the Home folder. The Launcher icon looks like this is the only existing Nautilus window. However, the other Nautilus window with the external disk unit still exists. You can reach it with Alt+Tab or by minimizing/moving other windows until it becomes visible.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: nautilus 1:3.18.4.is.3.14.3-0ubuntu6
ProcVersionSignature: Ubuntu 4.4.0-101.124-generic 4.4.95
Uname: Linux 4.4.0-101-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.1-0ubuntu2.13
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Dec 3 14:29:20 2017
GsettingsChanges:
 b'org.gnome.nautilus.window-state' b'sidebar-width' b'190'
 b'org.gnome.nautilus.window-state' b'geometry' b"'1257x861+330+87'"
 b'org.gnome.nautilus.list-view' b'use-tree-view' b'true'
 b'org.gnome.nautilus.list-view' b'default-column-order' b"['name', 'size', 'type', 'date_modified', 'date_accessed', 'owner', 'group', 'permissions', 'mime_type', 'where']"
InstallationDate: Installed on 2013-10-11 (1513 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
SourcePackage: nautilus
UpgradeStatus: No upgrade log present (probably fresh install)

[teo1978 (teo8976)]

I've realized the new window that is created when you open the external disk unit DOES have an icon on Launcher, which gets selected when it has focus and correctly shows the triangle(s) indicating its existing window(s). But it is separated from Nautilus' main Launcher icon.

This is a completely broken UI design. There's no reason to generate a separate icon in Launcher with a different symbol, and even if that made sense, there should be some kind of animation when this happens showing you that the existing window was destroyed and a new one has been created.
The overall user experience is inconsistent: if you look at the window you are interacting with, all seems like you keep using the same window, interacting with its contents which change. If you look at the Launcher icons, it looks like a new window has been created and the old one destroyed.