Grazie Nicola... Infatti era quello che stavo cercando.
Ho modificato il file purchase_view.xml in /addons/purchase come segue con l'intenzione che il mio ordine sia nella sezione RFQ solo negli stati draft e bid, mentre venga visualizzato nella sezione ordini in tutti gli altri casi.
Purtroppo non è cambiato nulla...
Devo aver quindi lavorato sul file sbagliato...
<record id="purchase_rfq" model="ir.actions.act_window">
<field name="name">Requests for Quotation</field>
<field name="type">ir.actions.act_window</field>
<field name="res_model">purchase.order</field>
<field name="context">{}</field>
<field name="domain">[('state','in',('draft','bid','cancel'))]</field>
<field name="view_mode">tree,form,graph,calendar</field>
<field name="search_view_id" ref="view_purchase_order_filter"/>
<field name="help" type="html">
<p class="oe_view_nocontent_create">
Click to create a request for quotation.
</p><p>
The quotation contains the history of the discussion/negotiation
you had with your supplier. Once confirmed, a request for
quotation is converted into a purchase order.
</p><p>
Most propositions of purchase orders are created automatically
by Odoo based on inventory needs.
</p>
</field>
</record>
<menuitem action="purchase_rfq" id="menu_purchase_rfq"
parent="menu_procurement_management"
sequence="0"/>
<record id="purchase_form_action" model="ir.actions.act_window">
<field name="name">Purchase Orders</field>
<field name="type">ir.actions.act_window</field>
<field name="res_model">purchase.order</field>
<field name="view_mode">tree,form,graph,calendar</field>
<field name="context">{}</field>
<field name="domain">[('state','not in',('draft','bid'))]</field>
<field name="search_view_id" ref="view_purchase_order_filter"/>
<field name="help" type="html">
<p class="oe_view_nocontent_create">
Click to create a quotation that will be converted into a purchase order.
</p><p>
Use this menu to search within your purchase orders by
references, supplier, products, etc. For each purchase order,
you can track the related discussion with the supplier, control
the products received and control the supplier invoices.
</p>
</field>
</record>