I was happy to find the Reader function available in my site, despite (or because?) of using HTML5, but suddenly it just disappear!. Lucky me I found the reason why very soon: Each inline comments should be a Div element, not an Article as it is in the default comment.tmpl.

Branchable sites do not use html5 by default. It sounds like you've turned on html5, which is why you're getting Article html elements. AFAIK we're using those elements in a standard-compatable way, so if you want divs instead you should disable html5.
Comment by joey Mon Mar 4 19:08:15 2013