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
move1 = self.env['stock.move'].create({
            'name': 'test_set_quantity_done_1',
            'location_id': self.supplier_location.id,
            'location_dest_id': self.stock_location.id,
            'product_id': self.product1.id,
            'product_uom': self.uom_unit.id,
            'product_uom_qty': 2.0,
        })
        move2 = self.env['stock.move'].create({
            'name': 'test_set_quantity_done_2',
            'location_id': self.supplier_location.id,
            'location_dest_id': self.stock_location.id,
            'product_id': self.product1.id,
            'product_uom': self.uom_unit.id,
            'product_uom_qty': 2.0,
        })
        (move1 + move2)._action_confirm()
        (move1 + move2)._force_assign()
        (move1 + move2).write({'quantity_done': 1})
        self.assertEqual(move1.quantity_done, 1)
        self.assertEqual(move2.quantity_done, 1)
    def test_initial_demand_1(self):