Hello, 

I'm trying to do the same  as here (https://www.odoo.com/forum/help-1/question/how-to-choose-form-view-used-by-many2one-field-in-openerp-v7-13709) but with res.users object, so this is my field:

<field name="user_id" context="{'form_view_ref':'base.view_users_form'}"/>

But it doesn't load base.view_users_form it loads base.view_users_simple_form, any ideas?