Encumbrance Reserve checkbox happen before or after approval?

Hello my Oracle friends.

I have a question regarding the Approval screen on PO documents.

When submitting a document for WF approval in the approve document screen there is a Encumbrance-Reserve check box.

This reserve will happen before the notification is approved or once its finally approved?.

I made a personalization so this checkbox is always marked, and now some PO documents are getting insufficient funds issue after the final approver approves the document, but i was expecting that if there are not sufficient funds in the charge account the "insufficient funds" warning would occur before trying to submit the document for approval.