Is it possible a NIC has a second address assigned? Check with
Alternately, is the machine responding via a NAT'd gateway? Try using a traceroute, and see if anything else is inserted into the path.
If neither are those are helpful, check the MAC address of that odd IP.
arp -a will show you all MAC/IP pairs, and
arp -a <IP> will do just one. Does that MAC address match one of the target NICs? If not, does it match any other machines? Perhaps something else is responding in its stead? Perhaps because you've accidentally assigned this server's IP to another machine?