Adding multiple IR items to the cart using catalogs

Summary:

The customer has a requirement to raise IR from browsing catalogs and request multiple items with their required quantities and add them to the shopping cart in one go, instead of following the traditional way of adding each IR line and selecting the source inventory and subinventory.

Now, while testing adding internally transferable items from the catalog to the cart, I had noticed that not item lines have the source set as inventory and the source field is not controlled where I can choose the exact source inventory. In addition, the subinventory field is not editable at all. Also, some item as per the attached has no source selected as inventory.