Preventing self-approval of released invoices

Hi,

We have predefined custom roles for approvers and assigned custom roles to users who are approvers.
But, when the person in charge sends the draft invoice, the “Approve” and “Reject” buttons are displayed on the user's screen.
It means that a user who is submitting the workflow can choose Approve/Reject himself.

We have already us an option in workflow configuration called "prohibit self-approval". So, we don't know why it happens.

The main issue is self-approval functionality. We still need to be able to handle requests from other users. Therefore, we cannot remove the privilage "Approve Project Contract Invoice" for the submitter.