jimbeetle - 5:31 pm on Aug 14, 2013 (gmt 0)
A link today is a vote for the page today. If you update the page tomorrow then yesterdays links are no longer as strong a vote for the 'new' content. It's the only thing that makes sense right now.
But then probably a bazillion other web folks would have noticed the phenomenon, not just you. Instead of a huge change in the PageRank algo -- which that would be -- I would chalk it up to something simpler, maybe along the lines incrediBill suggests, maybe something else.