Strange things can happen if you have two DHCP servers on the same network arguing about to whom to provide addresses.

The DHCP server in ARM won't respond to a DHCP request until the fifth retry (usually once a second), so the other DHCP server has to be really slow for this to be problem.

Also, if your PC booted using DHCP, it automatically turns off its internal DHCP server (on the assumption that you've got a functional DHCP server elsewhere). I think that it can be forced back on. I also recall that ARM doesn't detect this properly on older versions of Windows.

As you say, however, it is better to turn it off if you've already got a DHCP server.