Impacted versions: 9.0

Steps to reproduce:

* Create an MTO product with 
  * Product Type: Stockable Product
  * Routes: "Buy" and "Make to Order"
* Update Qty on Hand to any quantity (i.e, 2).
* Create a sales order with this product and a number <= to the one in the step before.
* Confirm the sales order.

Current behavior:

The created delivery picking appears in state "Reserved" and the current quantity on stock has been reserved, allowing you to transfer that stock.

Expected behavior:

The created delivery picking should be in "Waiting another operation", or at least in "Waiting availability" until the purchase order is confirmed (if you have defined a supplier for the product and the procurement creates the purchase order), which seems to be the current behavior when there's no stock available (is this also correct, as it allows to manually reserve?).
addons/stock/stock.py
continue
                        if not reserved_quant.lot_id:
                            false_quants += [reserved_quant]
                        elif float_compare(lot_qty.get(reserved_quant.lot_id.id, 0), 0, precision_rounding=rounding) > 0:
                            if float_compare(lot_qty[reserved_quant.lot_id.id], reserved_quant.qty, precision_rounding=rounding) >= 0:
                                lot_qty[reserved_quant.lot_id.id] -= reserved_quant.qty
                                quants_taken += [(reserved_quant, reserved_quant.qty)]
                                qty_on_link -= reserved_quant.qty
                            else:
                                quants_taken += [(reserved_quant, lot_qty[reserved_quant.lot_id.id])]
                                lot_qty[reserved_quant.lot_id.id] = 0
                                qty_on_link -= lot_qty[reserved_quant.lot_id.id]
                    lot_move_qty[move.id] = qty_on_link
                if not move_qty.get(move.id):
                    raise UserError(_("The roundings of your Unit of Measures %s on the move vs. %s on the product don't allow to do these operations or you are not transferring the picking at once. ") % (move.product_uom.name, move.product_id.uom_id.name))
                move_qty[move.id] -= move_qty_ops[move]
            
            if ops.pack_lot_ids:
                self._move_quants_by_lot(cr, uid, ops, lot_qty, quants_taken, false_quants, lot_move_qty, quant_dest_package_id, context=context)
            
            if not ops.product_id and ops.package_id and ops.result_package_id.id != ops.package_id.parent_id.id:
                self.pool.get('stock.quant.package').write(cr, SUPERUSER_ID, [ops.package_id.id], {'parent_id': ops.result_package_id.id}, context=context)
        
        move_dest_ids = set()
        for move in self.browse(cr, uid, ids, context=context):
            move_qty_cmp = float_compare(move_qty[move.id], 0, precision_rounding=move.product_id.uom_id.rounding)
            if move_qty_cmp > 0:  
                main_domain = [('qty', '>', 0)]
                preferred_domain = [('reservation_id', '=', move.id)]
                fallback_domain = [('reservation_id', '=', False)]