triggerfinger - 5:20 pm on Feb 6, 2012 (gmt 0)
the problem seems to happen when you remove a keyword that the page previously ranked for. It would seem that Google 'resets' the page as if brand new when keywords go missing
That is an interesting thought. I have a story that might support that theory. Specifically, after ranking high first page for years, Panda 1.0 shot my google ranking to the 5th page. However, our Bing ranking stayed strong.
After changing the Title Tag of my home page (mind you, the homepage was not the landing page that was ranking for the term), no only did my Google rank drop further into oblivion, but my Bing ranking as well.
Just one keyword, but it seems to support the "reset" theory.