Can be closed. Added this to Quick-CSS in the Theme:
I found the error. The plugin WP-HTML-Compression gave me that error. After deactivating it everything works.
I think I did not get you. The wordpress options and the theme options are not conflicting. Both are giving a static start page (start) and a blog page (blog).
I inserted the page blog in my menu. The page did not have any template assigned but my articles do not show up. I only get a result as in my screenshot.