I updated from Kubuntu 14.04 to 16.04 and after that, there is a mess within the calendar categories: there are up to 10 duplicates of each category I use.

I just experimented with a new test-category: If it's created, I can set a color and if an event is created with this category, the color is displayed correctly. But if I open the event again and look up the categories, the category is double, none selected - and the colour no longer displayed. In Settings > Manage Categories the category is also duplicated and deleting all up to one doesn't helped. Now, after some testing, there are ca. 10 times test-category...

What can I do?

If I look in my *.ics resource, the categories are stored as CATEGORIES: in plain text - all looks fine. In ~/.config/korganizerrc the categories are correctly (no duplicates) listed under [Category Colors2] - some with =invalid instead of something like =255,255,153 (colour, I assume). Where are the categories stored that are shown in Manage Categories?