The supervisor assigned to the user being searched is duplicated in the ca_contact table of the mdb database, causing the issue to occur.
1. Log into CA Service Catalog (or Service Desk Manager if is connected to same mdb database) as an administrator (ex: spadmin)
2. Administration > Users > Search for the supervisor of the user with the problem. Two duplicate users should appear.
3. Open one of the users and change the userid of this 'one of the 2 duplicates'.
4. Run the search again.
To search the duplicate users from database level in the mdb database/ca_contact table, see the document in the additional information section.