Prohibit Self Approval When single person in Approval Group

We are prohibiting Self Approval on Requisitions but got an issue / question around it

Our Setup is

Prohibit Self Approval - Ticked

Pre-Approval - Auto Approval

Header Approval - Send to Single person in Approval group.

Expected result - Reject the Requisition

Real Result - Approved

When Pre-Approval is turned off then the Requisition gets Rejected.

Or when there is multiple people in the approval group it goes to the other approver.

EG

Requisition - Naomi.Hayes

Pre-Approval - Auto Approve

Header Approval - Naomi.Hayes

Result - The Requisition gets approved but doesnt go to Naomi.Hayes

Requisition - Naomi.Hayes