Impacted versions:
11.0

I don't know if it is an issue, but I think is strange.

`product_qty` is in unit of `product` : https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L240
`reserved_availability` is in unit of `stock.move` : https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L295

`move.product_qty - move.reserved_availability` seems to have no sens, no ?

https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L915
https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L917
https://github.com/odoo/odoo/blob/11.0/addons/stock/models/stock_move.py#L924

thank for your answer

@jco-odoo 
@alnslang 


addons/stock/tests/test_move.py
ml.qty_done = 1
        res_dict_for_back_order = picking_pack_cust.button_validate()
        backorder_wizard = self.env[(res_dict_for_back_order.get('res_model'))].browse(res_dict_for_back_order.get('res_id'))
        backorder_wizard.process()
        backorder = self.env['stock.picking'].search([('backorder_id', '=', picking_pack_cust.id)])
        backordered_move = backorder.move_lines
        
        
        backordered_move._action_assign()
        self.assertEqual(backordered_move.reserved_availability, 0)
        
        lot3 = self.env['stock.production.lot'].search([('name', '=', "lot3")])
        backorder.write({'move_line_ids': [(0, 0, {
            'product_id': self.product2.id,
            'product_uom_id': self.uom_unit.id,
            'qty_done': 1,
            'product_uom_qty': 0,
            'lot_id': lot3.id,
            'package_id': False,
            'result_package_id': False,
            'location_id': backordered_move.location_id.id,
            'location_dest_id': backordered_move.location_dest_id.id,
            'move_id': backordered_move.id,
        })]})
        overprocessed_wizard = backorder.button_validate()
        overprocessed_wizard = self.env['stock.overprocessed.transfer'].browse(overprocessed_wizard['res_id'])
        overprocessed_wizard.action_confirm()
        self.assertEqual(self.env['stock.quant']._get_available_quantity(self.product2, self.customer_location), 3)
        self.assertEqual(self.env['stock.quant']._get_available_quantity(self.product2, self.pack_location), 0)
    def test_link_assign_10(self):