Hi Ben,
thanks a lot for responding. Both sides use the same css-files, the same plugins, the same design, there is nothing different with the exception of the text and the pictures within the text.
I found out, when I place the click-to-tweet at the end of the text, there ist no problem. But the more it goes up, the more the box grows.
I really have no idea and beg, that it is a tiny css issue..