I can now offer an explanation why I was experiencing the font size problems. In the old template the google benchnine:400 font was used for headlines. After the update that was changed to Arial-Helvetica.
This was responsible for the increase in size. After a lot of search and comparison I changed it back to the now availible font benchNine and it looked like before. So it was some update issue with the new template.
I am glad that I could fix it without editing the stylesheets.