Occasionally a MS DHCP delete operation fails
For reasons that have never been clear a netsh dhcp delete operation can fail for no obvious reason and give no error message. The operation claims to have completed correctly but the entry still exists. This class of problem was only ever see after the associated Microsoft DNS system was integrated into a federated forest but it may not be related to this issue.
If the operation was retried manually then the entry was always removed properly. This lead to a solution where we just performed all delete operations twice and that seemed to fix the problem. Note that it is only possible to delete a non-existent reservation. It is not possible to remove a non-existent lease without generating an error.