for any length of time you get to know its little quirks and foibles, and this is one of them.
I can't be absolutely sure, but I think you'll find that the FrontPage server extensions have glitched. When that happens the way to sort things out is to disable the extensions, re-enable them, and then republish the site. Almost invariably that will resolve the problem.
Many web-hosts provide a control panel on which you can disable and enable the FP extensions - otherwise you'll have to ask the host to do it for you. Doing the disable/enable will stop the web site from working, so don't forget to republish. If you have a discussion forum on the site it will almost certainly be out of sync with your local saved copy, so make sure that before you re-enable and republish you FTP into the server and transfer the forum message files to your site copy.