Hi Ingbert

I have one suggestion for you!  Try to do this in Odoo Studio (either use the demo database or download Odoo Enterprise and use as a trial), then you can see how Odoo handles this (which is as Zbik has explained):  

The Model (database table) will have a Name field and that is what will be displayed. If you delete the Name field you will get what you are seeing. 

Hello Zbik and Chris,

thank you for your advice! With rec_name it worked as expected, and finally, I settled upon implementing name_get, as I want to concatenate field values.

def name_get(self):
    result = []
    for record in self:
        result.append((record.id, "%s %s %s" % (record.first_name, record.middle_name, record.surname)))
    return result

Best regards!