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
self.assertEqual(move_stock_pack.state, 'confirmed')
        move_pack_cust._action_assign()
        self.assertEqual(move_pack_cust.state, 'waiting')
        
        move_stock_pack.write({'move_line_ids': [(0, 0, {
            'product_id': self.product1.id,
            'product_uom_id': self.uom_unit.id,
            'qty_done': 6,
            'product_uom_qty': 0,
            'lot_id': False,
            'package_id': False,
            'result_package_id': False,
            'location_id': move_stock_pack.location_id.id,
            'location_dest_id': move_stock_pack.location_dest_id.id,
            'picking_id': picking_stock_pack.id,
        })]})
        
        self.assertEqual(move_stock_pack.quantity_done, 0.5)
        
        backorder_wizard_dict = picking_stock_pack.button_validate()
        backorder_wizard = self.env[backorder_wizard_dict['res_model']].browse(backorder_wizard_dict['res_id'])
        backorder_wizard.process()
        self.assertEqual(move_stock_pack.state, 'done')
        self.assertEqual(move_stock_pack.quantity_done, 0.5)
        self.assertEqual(move_stock_pack.product_uom_qty, 0.5)
        
        move_pack_cust._action_assign()
        self.assertEqual(move_pack_cust.state, 'partially_available')
        move_line_pack_cust = move_pack_cust.move_line_ids
        self.assertEqual(move_line_pack_cust.product_uom_qty, 6)