okay I got it. I added something (cat span class part from the format.standart.php template) into my post.nosidebar.php and now it is also displayed in the posts. Don’t know if we took this out before. But it works.
I tried to understand your answer. Couldn´t find the information in the theme documentation (which document you exactly mean, the documentation.html in the zip?). I would also like to change this button.