Purchase order substitution

Hello,  I would like to see the ability to substitute on a purchase order while the order is open.  The PO section is missing on a few key points still which this is one of them.  NOrmally when ordering with a supplier, I am checking stock to order on their site.  While selecting items to be placed on the PO, I sometimes have to go back to an order to substitute an item.  I am already in the PO and the item does not automatically update.  I have to close out the purchase order and come back in.  This in turn brings up another miss with the way that the PO section works.  When I open a new PO, all of the items are checked.  This is the case when I first create the PO as well as when I try to add anything to a PO that was already created.  There is no break to see what was added or what was already placed on the purchase order.  I feel that nothing should be checked when beginning a PO.  I haven't ordered anything yet.  I have to un-check all, which is just an un-needed click.  Even more frustrating is when I add to a PO.  Everything comes in again as clicked, however I already placed items in my supplier cart and now I don't know what I placed in the cart and what I need to actually order.  Please address this on an upcoming update.