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Yes, i forgot to tell you i had to change the reference field lenght in database (from 9 to 16). 
The field is "reference" in table "orders" and "order_reference" in table "order_payment".

In addition it is required another file: override/classes/order/OrdperPayment.php
with following code

<?php
class OrderPayment extends OrderPaymentCore
{

  public function __construct($id = null, $id_lang = null, $id_shop = null)
  {
      self::$definition['fields']['order_reference']['size'] = 16;
      parent::__construct($id, $id_lang, $id_shop);
  }

}

Yes, i forgot to tell you i had to change the reference field lenght in database (from 9 to 16). 
The field is order_reference in the Tables order and order_payment.

In addition it is required also override/classes/order/OrdperPayment.php
with following code

<?php
class OrderPayment extends OrderPaymentCore
{

  public function __construct($id = null, $id_lang = null, $id_shop = null)
  {
      self::$definition['fields']['order_reference']['size'] = 16;
      parent::__construct($id, $id_lang, $id_shop);
  }

}