Messages still marked unread after reading

When I open an email, Outlook doesn't recognise that
the email has been read - Outlook still thinks it's unread
mail (bold text, etc). If I close the email and then open
it again, it *does* get set as read.

I'm not sure if this is a SpamBayes issue or not, but it
certainly didn't happen before I installed SpamBayes.
There may be some kind of wierd interaction going on
here (possibly involving specific Outlook settings? dunno).

For reference, I'm using Outlook 2000 (version
9.0.0.2711), and SpamBayes beta version 0.5 (July
2003).

Graham.