Thanks for keeping an eye open Tom! Let me know if you see anything strange again. I'll leave this here for a little while just to remind me to keep a lookout, then will remove it if it proves to be no problem.
BTW - I had a similar problem but it turned out that I was reading past the current page (when a board has multiple pages) and it stores the last page you were reading in the cookie. When you come back later, it brings the reader back to the page being read last. I just clicked on "page 1" and it brought me right back.