Hi Christine,
Not quite sure why it is happening.
Do you use the following link:
http://www.champdogs.co.uk/cgi-bin/board/forum.pl?
Try clicking it again. That should clear all new post flags. The only other thing I can think of is using your 'refresh' option on your browser? Failing that, maybe Mark will know.
You might find using the 'active topics' link a better option

It does the same as new posts.