Sam,
Are you seeing the <h1> tag appear on THIS page?
When I search the source code, I cannot find it. I do see the <h2> tag assigned to the topic title:
<h2>
<a href="/t/add-h1-titles-for-discourse-pages-seo/28106">Add H1 titles for Discourse pages (SEO)</a>
</h2>
It would be ideal to have <h1> be the one that has the title inside, since it's given more weight by search engines.