in the kde-core-devel thread "Kubuntu Settings in KDE" Riddell suggested setting NoDisplay=true on systemsettings.desktop, to prevent it appearing twice in the Computer tab, and in the Applications tab.

This solution goes too far, because you then cannot find the app with the search tool.

This patch adapts the Applications tab to ignore any apps that are configured to appear in the System tab, using a new static method in the Kickoff namespace to obtain the list in both System and Applications models.