I have a prestashop shop 1.6.x with 2 Warehouses.
It's using Advance Warehouse Management.
For a product you have available both Warehouses.
Product A - in Warehouse 1 = 10 products
Product A - in Warehouse 2 = 10 products
Right now once a order it's placed with 11 items of the same product from both Warehouses the order registers correctly but subtracts incorrectly and gives for the physical nr of items a negative number.
If the order's status get changed to "Shipped" the "negative" nr of items gets the stocks to the initial value as no order was placed.
Once the order it's placed it should subtract items from warehouse 1 and the difference between warehouse 1 and stock availability, from Warehouse 2.
So when the order it's placed no negative numbers have to be handled by the Advance Stock Management by subtracting between Warehouses.