Safari RSS annoyances

Safari periodically "forgets" which RSS articles I’ve read. This is a shame because suddenly all the articles I haven’t read get lost in a sea of articles that I really have read but which all at once have decided to mark themselves as unread. I have no idea why it does this but it is fairly annoying as it turns the RSS feature into a time drain when it is supposed to be a time saver. I hope they fix this soon.