In CRM 4.0 while running a duplicate detection job, you may see some records stating "Potential duplicate records: None" When running a duplicate detection job, some records are returned stating "Potential duplicate records: None"
In CRM 4.0, the records triggering the false positives in the duplicate detection job are marked for deletion, but they still exist in the database so they are discovered by duplicate detection.
Wait for the deletion service to run to eliminate these records. If the issue still occurs, verify that the deletion service is actually deleting records successfully.
Due to changes made to the Deletion Service in Microsoft Dynamics CRM 2011; this issue does not occur. Because of this, a hotfix for Dynamics CRM 4.0 will not be developed.