It's not flagging items that are unread, it's flagging items that are new since your "last visit". A "visit" times out after ten minutes, so if you have 3 news items flagged then close your browser and come back 30 minutes later (i.e. you generate a new visit), you won't see the flagged items anymore. It's actually not got anything to do with whether the messages are read or not. I find this timing-out of new messages a bit annoying too, though, so I've bumped the timeout to the maximum it can be, which is approx 27 hours. This will mean that your new message flags will last just over a day.

If you need to manually unflag your messages (i.e. you've read them), there's a link in the top-right of the homepage called "Mark all topics as read".

Charles, can I suggest an intermediate time-out length. With it on the maximum it now tells me there are new messages, when I have already read them the day before. Both extremes may causes problems so a time out period of 2 or 3 hours would seem reasonable to me.

Gordon