When you set Allow Backorders for Pickup setting is disabled, only the in-stock product is added back to the Cart
Steps to Duplicate
* Add two products to the cart, one in stock at the selected warehouse and one out of stock
* Switch the fulfillment method to PickUp
* Observe that the order can't proceed and the "Some of the item quantities in your cart are low in stock…" message is displayed in the Cart
* Save the Order
* Re-Add the Saved Order to the Cart
Observe that only the in-stock product is added back to the Cart
Desired Behavior is that both of the products should be re-added to the cart. The current behavior is a usability issue:
* There is no indication to the user that the out-of-stock product wasn't added back to the cart. This is a much bigger problem when there are more than a couple products being re-added (i.e., how is the user supposed to know what went into the cart and what didn't?.
* Management/removal of out-of-stock products should happen in the Cart itself. In the use case described above, the user initially gets the message in the cart telling them that there are out of stock products that they have to remove. If both of the products were re-added to the Cart upon re-adding the saved order, the user would see that one of the products is out of stock and needs to be removed/updated.