Always 1 unread mail notification smart folders

Since moving to V8, I see a bold “1” in “all inboxes” in smart folders, to indicate an unread email. This is not correct though, as there is no new mail to be found. “Mark all messages as read” does not change this. It does show new unread mails though, but always one to many. Looks like a bug to me.

So do I need to make a ticket first to get any answer? This is quite an annoying error, maybe I’d better go back to version 7…