Can you post the config, please?
I assume you've already checked the config and ensured you don't have a command like "no logging event link-status" listed?
I also assume you're getting other syslog events - just not the syslog events for the subinterface...
Do you have SNMP traps configured? Do you have SNMP traps configured to advise when the subinterface goes down?
Are you sure the router is sending them? (As opposed to are you sure the server is receiving the syslog info?) Might want to sniff the connection and ensure the syslog info is sent..!
