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?).
""" Splits qty from move move into a new move
        :param move: browse record
        :param qty: float. quantity to split (given in product UoM)
        :param restrict_lot_id: optional production lot that can be given in order to force the new move to restrict its choice of quants to this lot.
        :param restrict_partner_id: optional partner that can be given in order to force the new move to restrict its choice of quants to the ones belonging to this partner.
        :param context: dictionay. can contains the special key 'source_location_id' in order to force the source location when copying the move
        returns the ID of the backorder move created
        """
        if move.state in ('done', 'cancel'):
            raise UserError(_('You cannot split a move done'))
        if move.state == 'draft':
            
            
            raise UserError(_('You cannot split a draft move. It needs to be confirmed first.'))
        if move.product_qty <= qty or qty == 0:
            return move.id
        uom_obj = self.pool.get('product.uom')
        context = context or {}
        
        uom_qty = uom_obj._compute_qty_obj(cr, uid, move.product_id.uom_id, qty, move.product_uom, rounding_method='HALF-UP', context=context)
        defaults = {
            'product_uom_qty': uom_qty,
            'procure_method': 'make_to_stock',
            'restrict_lot_id': restrict_lot_id,
            'split_from': move.id,
            'procurement_id': move.procurement_id.id,
            'move_dest_id': move.move_dest_id.id,
            'origin_returned_move_id': move.origin_returned_move_id.id,
        }
        if restrict_partner_id: