arronsky - 12:36 am on Jun 25, 2010 (gmt 0)
What jim said. Google has written seemingly custom regular expressions for forums across the web. A minor change in your code can cause it to break and render the 1 post, 1 author thing (you'd think they'd have a filter in their code to not display when it's something as uninteresting as 1 post, 1 author, which to me means they actually WANT people to know/think your forum is stale and uninteresting and take it into account when clicking through results).
There is no recourse besides posting in the Google support forums and hoping someone pays attention, and no documentation about the feature exists.