If I 'read' or 'mark as read' an email from the 'Unread Mail' search folder the item in the Inbox is marked as 'read' and is what is expected behaviour though it can take up to 30 seconds for the item in the Inbox to be marked as read. If I 'read' or 'mark as read' an email in the Inbox it is NOT marked as read and remains 'unread' in the Inbox folder of the 'Unread Mail' search folder.
Since there are several unread messages exist in your mailbox, if necessary, please try to mark them as read and then test the result in that situation. 'Offline Settings' I have 'Use cached Exchange Mode' checked to 'yes' and 'Mail to keep offline' set to 'All' (Previously I had this set to 24 months) and the same behaviour is still being seen. Go to File > Account Setting > open your Exchange account > Adjust 'Mail to keep online' to 'All', restart Outlook to check the result.
