I’ve already tried this.
By now it seems, the problem is only with these two posts:
http://www.ptc-tests.de/clixsense
http://www.ptc-tests.de/neobux
I have noticed one strange thing:
When these two posts are the only ones in the category, then the top ratings show these posts.
As soon as there is another post in this category, these two posts are out of the top rating results and only the new ones are shown.
