Complex PO approved without supplier contact and payment terms (12.1.3)

All Experts,

Please review and advise.

1. We created a requisition and approved.

2. This was used to create a new complex PO using document builder.

3. Complex PO is created and without any changes, sent for approval and it gets approved. At this point, it did not have supplier contact, description, payment terms etc filled and still it got approved.

4. When we try to update this complex PO now, it gives validation errors for supplier contact, description, payment terms information missing as this is mandatory.

My question - Why did oracle allow to submit and get complex PO approved when some mandatory information was missing ?