Hi I am having the same problem which has been occurring for almost a year. This does not appear to be a wifi problem. When I disconnect my router from the internet but keep my wifi running then the bogus phones disappear. when I connect back to the internet within a few hours they reappear. Even when i connect via cable to the internet with WIfi switched off they still appear. This would explain the no IP.
I would strongly disagree with those that say it is is not a security problem. Any unknown device that can write to my laptop or pc is a security problem. The fact that it was able to write its MAC address in the memory of my PC means that it has access in some form to my PC. It may be limited to just that but no one has come up with any valid explanation as to what is going on and this should be treated as a valid security threat. Those that are trying to say that it is not need to check out the facts. In my case, and it appears it be the same as everyone else it is not wifi but internet related