komparator4 does not show duplicates when they really exist

[Norbert]

Steps to reproduce:
1. Install Ubuntu 16.04 LTS / 17.10 / 18.04 LTS
2. Install komparator package
3. Create folder with duplicates and launch duplicates search here:

mkdir /tmp/komp
cp /etc/os-release /tmp/komp/
cp /etc/os-release /tmp/komp/os-release2
komparator4 /tmp/komp/ /tmp/komp/

4. Do not touch options in komparator4 window and click *Search* button.

Expected results:
* komparator finds duplicates

Actual results:
* komparator does not show duplicates, produces the following text in terminal

Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
kbuildsycoca4 running...

Notes:
1. This problem was discovered on AskUbuntu by Hein Bloed - see https://askubuntu.com/q/970465/66509 .
2. I do not know why, but komparator does not work only on clean install.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: komparator 4:1.0-2
ProcVersionSignature: Ubuntu 4.4.0-98.121-generic 4.4.90
Uname: Linux 4.4.0-98-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Nov 5 13:29:35 2017
InstallationDate: Installed on 2017-11-02 (2 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: komparator
UpgradeStatus: No upgrade log present (probably fresh install)

[Norbert (nrbrtx)]

Still does not work on clean Ubuntu 16.04.4 LTS amd64 with all updates and empty output of `debsums -s -a -c` (system integrity check passed).

[Launchpad Janitor (janitor)]

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