Old non-existent pages suddenly return !!

[Spooky]

Hi all,

I have become somewhat confused - I recently re-wrote some pages on my web site and put 301 redirects on the old pages - very quickly the new pages started getting ranked and did quite well, especially on yahoo - of course, page rank for those pages went from 5 to zero (woohoo!!!) - here is the thing though - over the weekend the new pages have disappeared from the search engines for the most part and are showing up as the old pages (with the old content, titles etc) - Does anyone have ANY idea what that is all about?!?!