Changes/edit to Purchase Order reference numbers do not automatically reflect in the Purchase invoice Tab Until the Invoice is opened for editing.
I believe when order numbers are changed, it should automatically reflect in the Purchase invoice tab where the order number is displayed for the related invoice. I could not reproduce this for Sales Orders.
Also, on the actual Purchase invoice, the purchase order reference number does not appear.
I think I did not make myself clear. I meant to say the Order reference number does not automatically reflect in the purchase invoice tab after it (reference number) has been edited. I have edited the original post, I hope it clearer now.