Contract Purchase Agreements released amount query

We are using R12.1.3 and have created a CPA which we are calling standard purchase agreements off against.  We have high value standard purchase orders that have already been called off against the CPA. If we make a revision to these standard purchase orders, for example, adding a second line for 1K which is within the remaining agreed amount of the CPA we are receiving an error advising we are exceeding the limit of the CPA.

My question is, if we create a revision of a high value purchase order will Oracle look at the total amount of the PO and compare to the amount remaining on the CPA or will it take the incremental changes? My understanding is that the PO will be treated as a new commitment and therefore the full amount of the purchase order will be called off from the CPA.