Incorrect inventory when checkout item in different warehouse & setting Allow Preorder/ backorder = True

Steps to reproduce

Precondition: Config itemA for 2 warehouse that is in store pickup, (ex: set Hanoi and Bangkok as In Store Pickup). see attachment for more detail

1.Checkout 3 item A, select ware house = Hanoi. Checkout successfully

2. Go to order system, open the above order detail/ click on New Line Item to edit order/ Add again itemA but select it in Bangkok store.

3. Add payment then confirm OK. Observe that now order updated successfully

4. Go to Catalog system/ Check inventory on Bangkok  store --> Observe that inventory not deducted.

Check inventory of Hanoi store --> Observe that it deducted according the number of item at step 1 + step 2

Expected: the inventory deducted according to action at step 2 for Helsinki store

The inventory for Hanoi store is correct as at step 1

NOTE that: system will deduct qty in 2 WH correctly in case setting Allow Preorder/ backorder = False