Problem/Glitch with unread mail and going back to inbox --- missing emails


Outlook version
Outlook 2007
Email Account
Exchange Server
Hello everybody, one of my employees has this rather strange issue. If he is in his unread mail and clicks back to Inbox, it is completely empty. Once he clicks on sort by recieved, everything comes back up. He then sorts by date and arranges back his emails.

Is this a common or known glitch? I've tried to search for a resolution and cannot find one. I have tried the MS Office repair/diagnostic tool and it found and repaired on issue this morning but it still is comming back.

Any ideas?