MythBuntu (and Ubuntu I assume) don’t support the AutoIP standard.
(Auto IP is basically a way for devices to form ad-hoc networks…if you don’t have a static IP, and are not assigned a dynamic IP via a dhcp server, you try out a random address in the 169.254.x.x network (255.255.0.0 netmask) and as long as ARP doesn’t report a conflict, you now have your IP!)

Windows, and the HDHomeRun devices support this, but MythBuntu 9.10 does not. So, I’m back to using firestarter to easily configure my MythBuntu box to assign the HDHomeRun an IP address via DHCP.