AFAIK nmdb does only work correctly, if the right IP addresses are entered into the hosts configuration file. And maintaining the hosts file means using static IP addresses or at least assuring that DHCP always give the same IP address to each computer. Having wrong IP addresses in your hosts file might lead to your problem.
I don't see the benefit from using DHCP on a home network anyway. Even on Windows, DHCP needs around two minutes to determine the network address. With static IP addresses the network is up and usable at once.
Bye,
Thomas
