@Toni: This theme in build in HTML5 and CSS3. As per the HTML5 guideline, you have have one h1 tag in every article header tag. I understand this was issue in HTML4 but not in HTML5.
Multiple H1 is allowed in HTML5 and we have carefully designed H1 tags with special attention on header tag and headings. You can also check this Video http://www.youtube.com/watch?v=GIn5qJKU8VM by Google software engineer Matt Cutts, who clearly states that you can use multiple H1 but don’t over do it. Also use h1 specific to heading and header tags.
You can also check this article URL http://html5doctor.com/html5-seo-search-engine-optimisation/
Also check out the default theme by WordPress also uses multiple H1 http://twentytwelvedemo.wordpress.com/
I hope now you are clear.
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