How to generate my own create button in a form?

I have created a button of type action. This button calls an action, and this action calls a form. This form was totally created by me, and has a Create button, which calls the create function, directly inherited from orm.Model (I did not touch it).

When I click on Create, the record is perfectly stored on the database, but then I get this error:

File "/opt/openerp7/openerp_70_ocb_devel/ocb-server/openerp/osv/orm.py", line 4342, in create if vals.pop(f, None) is not None: TypeError: pop() takes at most 1 argument (2 given)

I was looking for the content of vals, and when I click on the button, the create method seems to be called twice. The first time, vals brings the values of the record in a dictionary (all right), the second time brings the ID of the new record generated in a list, and provokes the error.

I would like to know why is this happening and how to solve this. I left here my code:

The button which calls the action:

<button name="%(res_partner_extended.action_create_res_partner_link_category)d" string="Link to category" type="action"/>

The action:

<record id="action_create_res_partner_link_category" model="ir.actions.act_window">
    <field name="name">Link to a new category</field>
    <field name="type">ir.actions.act_window</field>
    <field name="res_model">res.partner.link.category</field>
    <field name="view_type">form</field>
    <field name="view_mode">form</field>
    <field name="view_id" ref="res_partner_link_category_create_form_view"/>
    <field name="target">new</field>
</record>

And the form, with the button which is getting the error:

<record id="res_partner_link_category_create_form_view" model="ir.ui.view">
    <field name="name">res.partner.link.category.create.form</field>
    <field name="model">res.partner.link.category</field>
    <field name="type">form</field>
    <field name="arch" type="xml">
        <form string="Linked category" version="7.0">
            <group>
                <group col="2">
                    <field name="partner_id" readonly="1" options="{'no_open': True,}"/>
                    <field name="link_category_id" required="1" options="{'no_open': True}"/>
                    <field name="type" required="1"/>
                </group>
                <group col="2">
                    <field name="date" required="1"/>
                    <field name="observations"/>
                </group>
            </group>
            <footer>
                <button name="create" string="Create" type="object" class="oe_highlight"/>
                or
                <button string="Discard" class="oe_link" special="cancel" />
            </footer>
        </form>
    </field>
</record>