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 


""" In a situation with a negative and a positive quant, reserve and unreserve.
        """
        q1 = self.env['stock.quant'].create({
            'product_id': self.product1.id,
            'location_id': self.stock_location.id,
            'quantity': -10,
            'reserved_quantity': 0,
        })
        q2 = self.env['stock.quant'].create({
            'product_id': self.product1.id,
            'location_id': self.stock_location.id,
            'quantity': 30.0,
            'reserved_quantity': 10.0,
        })
        self.assertEqual(self.env['stock.quant']._get_available_quantity(self.product1, self.stock_location), 10.0)
        move1 = self.env['stock.move'].create({
            'name': 'test_unreserve_6',
            'location_id': self.stock_location.id,
            'location_dest_id': self.customer_location.id,
            'product_id': self.product1.id,
            'product_uom': self.uom_unit.id,
            'product_uom_qty': 10.0,
        })
        move1._action_confirm()
        move1._action_assign()
        self.assertEqual(move1.state, 'assigned')
        self.assertEqual(len(move1.move_line_ids), 1)