Months ago I applied a new subnet mask to my network, allowing more hosts. I took the IP addresses in question from the dynamic DHCP scope and assigned them as additional static addresses. Today, I find that nslookup for IP addresses in the decommissioned dynamic scope shows me the hostname of a DHCP node that is actually at a different IP in the new dynamic scope. The node I assigned as a static IP in this new static scope (the decommissioned range of my dynamic scope) shows the hostname that could only have come from a lease in the old network instead of the correct hostname.
The DHCP configuration on a Windows Server2008R2 domain controller looks right, but something got missed. This is the only server in the domain with that role.