A DHCP client (ie the roboRIO) is able to ask for a specific IP address. In this case, the roboRIO probably asked for it's old IP address, and if that address was still in the valid range, the dlink DHCP server probably assigned it. If you changed the dlink to serve a completely different range, eg 220-230, I would expect the roboRIO to change. Does this match the behavior you're seeing?
The dlink supports DHCP address reservation, where the server will always give out the same address to one device. You can read about it on page 30 of the manual:
http://www.dlink.com/-/media/Consume...l_v2_10_EU.pdf