This is normal for Routing and Remote Access. I would make sure that RRAS is not configured for VPN access as this service will grab a number of IPs to make sure VPN clients have some available.

To get to the core of your problem, as stated before, turning off DDNS on the NIC and adding the DNS record manually on the DNS server should work, as long as it's not a domain controller. You can change the DDNS setting in the advance TCP/IP properties of the NIC.

Hope this helps.