ghost connections

Why is is we are experiencing ‘ghost connections’ ie a user has 1 login entitlement, they are no longer logged in (having browsed thru our servers) yet NWAdmin shows under users details a ‘network address’ entry which prevents the user logging on. We then have to up the max connections to 2. Only once the user is currently logged in can we delete the unwanted ‘network address’. Does anyone have clues on removing this unwanted entry.