I have a model called loan.application:

from openerp import models, fields, api, exceptions, _

class loan_application(models.Model):
    _name = 'loan.application'
    _description = 'Loan Application'

    partner_id = fields.Many2one(string="Partner", comodel_name="res.partner")
    partner_title = fields.Many2one(related="partner_id.title")
    partner_name = fields.Char(related="partner_id.name")
    partner_street = fields.Char(related="partner_id.street")
    partner_street2 = fields.Char(related="partner_id.street2")
    partner_city = fields.Char(related="partner_id.city")
    partner_zip = fields.Char(related="partner_id.zip")
    partner_phone = fields.Char(related="partner_id.phone")
    partner_mobile = fields.Char(related="partner_id.mobile")
    partner_email = fields.Char(related="partner_id.email")

I have a form view that displays all these fields.

Now, the weird part:

If I fill out all of these fields and press the [Save] button, all the related fields are saved, except for: partner_street, partner_street2, partner_zip and partner_mobile. What makes these four fields so special that they do NOT save?