The service reserveProductInventoryByFacility (file InventoryReserveServices.xml) simply do nothing in case quantityNotReserved value is not 0, but (ProductStore) requireInventory = Y.
Now, no action is taken and quantityNotReserved is simply returned to the caller (ie: reserveStoreInventory).
In this scenario an order can be placed despite there is no available inventory to fulfill an order item, causing backorder (that we wanted to avoid setting requireInventory flag on the ProductStore to Y ).
I checked the usage of the service around the project and it seems to me that we can make an important assertion: we can consider that also requireInventory flag of the ProductStore is Y.
This issue is strictly related to