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
""" Send 5 tracked products to a client, but some of these products do not have any lot set
        in our inventory yet: we only set them at delivery time. Adding a lot_id on the move line
        that does not have any should not change its reservation, and validating should not create
        a negative quant for this lot in stock.
        """
        lot1 = self.env['stock.production.lot'].create({
            'name': 'lot1',
            'product_id': self.product3.id,
        })
        lot2 = self.env['stock.production.lot'].create({
            'name': 'lot2',
            'product_id': self.product3.id,
        })
        
        self.env['stock.quant']._update_available_quantity(self.product3, self.stock_location, 3)
        self.env['stock.quant']._update_available_quantity(self.product3, self.stock_location, 2, lot_id=lot1)
        
        move1 = self.env['stock.move'].create({
            'name': 'test_in_1',
            'location_id': self.stock_location.id,
            'location_dest_id': self.customer_location.id,
            'product_id': self.product3.id,
            'product_uom': self.uom_unit.id,
            'product_uom_qty': 5.0,
        })
        self.assertEqual(move1.state, 'draft')
        
        move1._action_confirm()