a few years ago when I swapped out servers with DHCP roles I had servers picking up settings from 3 DHCP servers before then even though those DHCP servers were turned off. they weren't actually getting addresses from the old DCHP server but filling in settings that the server would have passed out. even though when you did ipconfig / all it was showing the correct DHCP server. drove me mad for several days and I honestly can't remember what it ended up being....