Prestashop 1.7 customer custom fields strange behavior

Question

I added two new variables to the ps_customer database and in customer class:

/** @var string ricetta */
public $ricetta;

/** @var int agente */
public $agente;

And in the definition array:

        'agente' => array('type' => self::TYPE_INT, 'size' => 11),
        'ricetta' => array('type' => self::TYPE_STRING, 'required' => true),

All is perfect; I can manage these fields in the admin area and in general in the whole environment.

But something very strange happens when on the frontend PasswordControllerCore is called.

I discovered that when $customer->update(); consumed, one of two new fields ($ricetta) in database became empty.

The Customer update delete this, but not the other custom field.($agente)

I'm becoming crazy for that ...no way to understand what happening :-(