Empty string property on ShipmentListItem From and To location number

When using the ShipmentList.GetShipmentList(DateTime.Now.AddMonths(-1), DateTime.Now) method in the Avontus.Rental.Library, my ShipmentListItem objects have empty strings for the FromLocationNumber and ToLocationNumber properties.

But when I use the method ShipmentList.GetShipmentList(TradingPartnerId, ShipmentStatusType.ShowAll, false), my ShipmentListItem objects do contain values for the FromLocationNumber and ToLocationNumber properties.

The documentation does not mention anything about this behavior. Can anyone explain why these properties are returning empty strings instead of actual location numbers when using ShipmentList.GetShipmentList(DateTime.Now.AddMonths(-1), DateTime.Now)?

I just discovered that ShipmentList.GetShipmentList(DateTime.Now.AddMonths(-1), DateTime.Now) doesn’t return reservations. Why does the ShipmentListItem result from ShipmentList.GetShipmentList(TradingPartnerId, ShipmentStatusType.ShowAll, false) differ from the ShipmentListItem result of ShipmentList.GetShipmentList(DateTime.Now.AddMonths(-1), DateTime.Now)?