Yesterday, I added the Co-authors plus plugin to my site, and it seems to work properly. But there is a strange side effect.
Now, on the author pages, I show a list with all the articles of the specific author. But at some author pages, the articles are displayed multiple times:
See an example here: http://sargasso.nl/author/jaap-walhout/
The strange thing is that these articles are not written by multiple authors, and the author is never used as a co author. Also, the author page of other authors displays just ok. See: http://sargasso.nl/author/joost/ (this author is used as a co-author)
http://sargasso.nl/author/ad-van-der-stok/ (this author is not used as a co-author)
Any clue? I am using a plugin to combine multiple content types in the list.