On the process of managing items on a warehouse is required to mark some locators to be excluded from the count and from the process of demand operations, like reservations, assign for shipping, movement replenishment, etc.
See http://wiki.idempiere.org/en/FS_Exclude_Locators_for_Demand_Operations for complete specification.
We have a use case when users try to save Customer Return line where locator have type with IsAvailableForShipment='N'. This will not allow to return products on locators such as this.
I suggest to check if Locator is Available for Shipment in InOutLine only if it is Shipment (C-) instead of checking if it is Sales Trx.
See attached patch.
Thanks , committed your patch