Open Items list not showing amount, net, and tax

Hi all

We have a client who has partially copied a Sales order to a delivery. He normally uses the copy to function from the sales order. In the delivery, he changes the quantity of the item that is out of stock to 0. When he opens the open items list, there are a few SOs that show as open but do not show the amount, net, and tax figures. This isn't the case with all of the orders.

I have checked the forums and one of the answers says that it is system behavior. Why is it that some of the open SOs on the report show the figures and some don't?

Any help would be appreciated.

Thanks
Jeff