Correction. I can't save my edited version so I'll put it this way instead.

Here is the scenario to reproduce the issue:

1. I have a product (Product 1) and the current stock is 10 quantities in WH/Stock.

2. I did an internal transfer from WH/Stock to WH/Stock/Dep - 1 qty of Product 1

3. The current stock of Product 1 is 1 qty in WH/Stock/Dep and 9 qty in WH/Stock.

4. I created a sales order with 1 qty of Product 1 and view the delivery order.

5. I clicked on the Check Availability button and upon checking on the reserved quants, the item that was reserved is from WH/Stock/Dep although the Source Location indicated is from WH/Stock.

6. When I clicked on Transfer button, the Source Location is WH/Stock/Dep instead of WH/Stock. (I think the reason behind this is FIFO method, please correct if I'm wrong)

7. So I changed the source location from WH/Stock/Dep to WH/Stock and clicked Apply button.

8, I checked the current stock of Product 1(Product From - Current Stock View smart button) but the view shows only the stock from WH/Stock and the location WH/Stock/Dep is missing.

9. When I check in Current Inventory Valuation menu and filter the Product1, it shows that in WH/Stock (8 qty) and in WH/Stock/Dep (1 qty) which is right since I changed the source location in the Transfer wizard.

The two views are showing different information. I also checked the Warehouse > Configuration > Locations > WH/Stock/Dep > Current Stock but there's no available product which is wrong. There should be one available quantity of Product 1.

I tried this on a default database without any custom modules installed. Will someone explain why this is the behavior of Odoo? Is this a bug?