I had my main Genie unit change its IP address.  It was reserved in the router outside of the dhcp pool, then one day I lost control of it and found that the receiver had a new address within the dhcp pool.  upon further inspection, it had a different MAC address.  To my knowledge, this unit doesn't have wifi capability.  It was/is connected to the network using the Cinema connection kit/MoCa.  I was not using the ethernet connection on it.  That might have played a part in this.