This is my first ever post...!

I am newish to DAX, mainly financials 2012, r2 and r3.

An existing support client has raised the following issue:

PO created for product. Ordered 1 tonne, received 2 T.

Client receive 1 of 2 Purchase invoices (Each invoice is for 1 Tonne of product).

On processing the 1st PINV they post by selecting  parameter quantity "Delivery Note" update amount to 1 T and process. (They also had credit negative quantity tick box selected in other tab). They were not aware of this. 

On receipt of second invoice, they tried to process again using the original delivery note, and obviously they had closed it due to the above.

To process the 2nd invoice, they processed:

1. Created a new po line for the product (1 Tonne) receipted and posted invoice.

2. In addition to the above they also posted a negative quantity "Delivery Note" on the original PO line for the product (Quantity tab on the PO line, entered -1 T, and posted delivery note).

The result of the above is that the PO status is now received. From a financial and physcial stock perspcetive all appears to be correct however the posting of the negative amount means that DAX is waiting for the negative amount to be credited.

I have read through a lot of material as to how to correct this and I have failed. Any help greatly appreciated.