I knew that would get your attention.. setting boot-device to enet:0,bootme goes to the first most powerful dhcp server it can find, who doesn't happen to have the bootfile, and so it seems to release that OFFER and then goes to the next dhcp server who was waving the file around in an OFFER and accepts that offer instead.
I think this is how the MacOS netboot server is supposed to work as well because it supposedly coexists with any existing dhcp server. I am using a private dhcp server on 192.168.x.x with deny unkonw clients set to true and mac addresses configured in /etc/dhcpd.conf. Seems to work just fine. As if it was almost engineered to be this way. Jeepers considering all the trouble I had trying to get it to accept enet:my.tftp.server.ip,bootme and enet:0,bootme with default-gateway-ip=my.192.dhcp.server it is amazing this works so smoothly. Peter