Prohibit self approval does not work if that preparer is the only member of the approval group

Summary:

Hi,

We have several groups where there is only one member within an approval group.

When that member in the approval group is the preparer, the requisition will be approved automatically.

We have set 'Prohibit Self Approval' on the approval task.

What should be happening is the requisition rejects if the preparer is the only member in the approval group as we are prohibiting that member from self approving. There is no one else in the group to approve.

Is there any other setting we can look into to ensure these types of requisitions are rejected?