I set the plugin to show the related posts which have at least one category and one tag in common. When I created the posts (let's say 5 posts) within one category and one simular tag, I check if every post has the same related posts (4). After clicking one of the post in the related list I get a post which shows only 1 related post. When I re-save this post I see all the related posts (4) of this category.
So I must re-save every post to get the correct output.