Put a new client on Thunderbolt, and found that an IP address associated with the Routing & Remote Access (or VPN Server) IP address was displayed for a Windows SBS 2003 server that was discovered. However, the MAC address associated with the server was the MAC address of the NIC, which had the right server IP address. The VPN IP address displayed a different (and invalid) MAC address on the server, but that MAC address wasn't being discovered by the TBA.
Tried adding the IP address with the right MAC address, but that didn't work. And I couldn't forcibly change the IP of the device discovered.
When I rebooted the server later, the right IP and MAC address now come up in the TBA, so all is good.
As a side note, I thought there was a way to associate multiple MAC addresses/IP addresses with one device, like a laptop with wireless and an Ethernet connection, no?