I have a setting in a theme fragment that is not saving (I think since self.data['kontent_type'] returns '' no matter what I choose. All the other fields save OK and I see no errors.
After basically giving up last night, I found some old code in another fragment and tested that.
It worked.
After duplicating that fragment, the duplicated fragments did not work, and I discovered that it was because of the name
Turned out that if a fragments has a name with '-' in it, it will not save this field correctly. All other fields saved OK.
So, simply changing my fragment from
news-copy.xml (.pt / .py) to news_copy.xml it works
( I had used duplicated working templates, and the OS gave them a name with '-'