This blog post has comments powered by a discourse topic. In my reply to the topic, I included a link to a youtube video. It is not appearing below the blog post in the comments, while it does show up in the accompanying discourse topic. I think this is a bug because I expect it to appear in both places. If onebox is not supported, at least it should display the URL to the embedded content.
Screenshot of comment in blog:
Screenshot of comment in discourse: