Odoo 8 strange behavious using new api to inherit old api model

Question

I added two fields to stock.picking using new api:

class StockPicking(models.Model):
    _inherit = "stock.picking"

    address = fields.Char(related='partner_id.street', string="Address")
    sector = fields.Char(related="partner_id.sector", string="Sector")

Then I added onchange method to load stock pickings in One2Many field defined using tree:

<field name="line_ids" >
    <tree>
        <field name="name" />
            <field name="partner_id" />
            <field name="address"/>
            <field name="sector"/>
            <field name="state" />
        </tree>
</field>

I used a simple domain with search [('id', '<', '10')] then I changed line_ids value but no line was loaded in the web view.

After many times trying to find a log error with no success I changed the code from the new API to the old API:

class StockPicking(osv.osv):
    _inherit = "stock.picking"

    _columns = {
        'address': fields.related('partner_id', 'street', type='char', relation='res.partner', string='Address'),
        'sector': fields.related('partner_id', 'sector', type='many2one', relation='sector', string='Sector')
    }

For a reason that I do not know It worked.

Did someone know why this did not work using the new API?