Cannot install global Themes: kf.newstuff.core: "/usr/share/knsrcfiles/colorschemes.knsrc" doesn't contain a KNewStuff3 section

Hi there,

I recently have problems with installing global themes. Before Plasma 6 I had a great collection of themes, now they are beginning to appear as ported versions and I like to install them again.
But some of them fail, stating the following:

kf.newstuff.core: "/usr/share/knsrcfiles/colorschemes.knsrc"  doesn't contain a KNewStuff3 section.

Is this already known? Is there something I can do?