Invoice approval

12.1.3

What would cause an invoice to be auto-approved by the final approver without the person approving the invoice. there are three approvers setup to approve invoices based on approval limits. the first and second approver approves the invoice. when the final approver log in to approve the invoice is not in their workflow to approve. when i check the invoice workbench approval form form the invoice is reflected as approve by the final approver.

I log an SR and base on the information they requested, they are saying the user ID and the user name is not the same for the final approver. It is showing the User Name for the Final approver and the User ID for the second approver.