You, as a personnel administrator, find that the Manager field in employee's personnel file actually shows the Reporting Line Unit manager of the employee, who may be different from his/her Cost Center manager.
This is expected system behavior. Because, the personnel file always displays the Reporting Line unit not the Cost Center Manager.
If you flag an org unit as a reporting line unit then the manager of the org unit is a personnel manager. A personnel manager is responsible for employees’ work center assignments, personnel-related tasks, and purchasing approvals.
If no manager is assigned to a reporting line unit, the manager assigned to the next reporting line unit above it in the org structure takes on the responsibilities of the personnel manager.
KBA , SRD-MD-OM , Organizational Management , How To