users have to keep adding back the unread folder in outlook to the search folders, it also removes it from the favorites list?

On frequent occasion our users (who mainly use Outlook 2010), have to add the unread folder back into their search folders.

They also have to then re-add it as their favorite (if they use the favorites list, most do).

Why does this happen on our exchange server accounts?

I notice the unread folder (and favorite  listing) for any PST archives in their Outlook remains.

Ant0