Rick_M - 3:45 pm on Mar 5, 2010 (gmt 0)
I don't have a news site but it sounds like something Google would want to intentionally do in order to keep a news article from showing up twice on the front page. If an article is eligible for the section of related news articles, they wouldn't want it to also appear in the regular organic results.
After it is no longer eligible for recent news, it then becomes eligible for the regular organic serps.
This is pure speculation on my part but it seems logical from Google's point of view.