Planet13 - 3:36 pm on Aug 10, 2013 (gmt 0)
If it were simply google not trusting pages with content additions, then how would that affect pages that allow blog commenting? Because it would seem to me that it would be a similar scenario: a site ranks well, and (from time to time) new content is added.
Personally, I don't believe that the rank modifying patent is in use by google as much as others do. I am sure it is used, but I don't know think its use is as widespread as others believe.
My first thought is that maybe you tripped some sort of over optimization trigger for a particular keyword or keyword phrase.