Can't change file associations in KDE system settings

[Fibonacci]

After a fresh install of Kubuntu, I found JPEG files opening by default with Firefox, instead of with some more sensible application such as Gwenview. So I opened systemsettings5, then clicked on Applications, File associations, located image/jpeg and moved Gwenview to the top of the list.

For some reason, $HOME/.local/share/applications/mimeapps.list is modified appropriately, but JPEG files are still opening with Firefox. What's more, right clicking on a JPEG file and opening the “Open with” menu, I found it hadn't been modified at all, no matter what I did on system settings.

Choosing “Other...” in the aforementioned menu then selecting Gwenview and remembering the association succeeds in getting all JPEG files to open with Gwenview, but the applications list in system settings is not modified.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: systemsettings 4:5.2.2-0ubuntu1
Uname: Linux 3.19.8-031908-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.2-0ubuntu1.2
Architecture: amd64
CurrentDesktop: KDE
Date: Sun Aug 9 16:43:13 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-07-13 (27 days ago)
InstallationMedia: Kubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: systemsettings
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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

[Paul White (paulw2u)]

We are sorry that we do not always have the capacity to review all reported bugs in a timely manner. You reported this bug some time ago and there have been many changes in Ubuntu since that time.

Ubuntu 15.04 (vivid) reached end-of-life on February 4, 2016.

Do you still see a problem related to the one that you reported when using a currently supported release of Ubuntu? Please let us know if you do otherwise this report can be left to expire in approximately 60 days time.