e have seen his many times and apparently it is a bug in the FP extensions that has yet to be fixed.
When you edit a page that has a FP visitor counter on it the counter resets to 0 for no real reason.
Solution: Simply go into the page with FP, right click on the counter to bring up the counter menu and select the reset number box. Once you save the page the counter will start over at whatever number value you entered.
You may also run into problems if you try to include the counter within an "include page" like a footer.