MAC address substitution

A user of my imp-enabled product is unable to connect his device from home. We suspected that his router was blocking port 31314 but he is able to successfully telnet to 31314 on the network in question. He ran wireshark, and found that the downstream communication from imp servers to his device has the wrong MAC address. The MAC ID of his imp is 0C-2A-69-0A-71-BB but the downstream communications are associated with a Cisco device with MAC ID C4-71-FE-73-1A-E2 (user has no such device). Any thoughts on what is going on?

I looked at the pcap and this appears to be a local router issue. The imp is sending identical SYN packets in both cases (well, different local port numbers as expected) but when it doesn’t work, the reply from the imp server has been routed to a bogus mac address by a totally different local router.

Summary is that it’s unrelated to the imp, and very much related to the local network environment as proved by the pcaps.