i added a new state 'sourcing' and a button to change state to sourcing .. when i click the button state changes to sourcing in states bar but the problem is my quotation changes to sales order

how can i stop this

#state adding

<record id="sale_order_custom_state" model="ir.ui.view">
    <field name="name">sale.order.form.changed</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="priority">1000</field>
    <field name="arch" type="xml">
        <xpath expr="(/form/header/button)[1]" position="before">
            <button name="sourcing" states="draft" string="Sourcing" type="object" class="oe_highlight" />
            <button name="action_quotation_send" string="Send by Email" type="object" states="sourcing" class="oe_highlight" groups="base.group_user"/>
            <button name="print_quotation" string="Print" type="object" states="sourcing" class="oe_highlight" groups="base.group_user"/>
            <button name="action_button_confirm" states="sourcing" string="Confirm Sale" type="object" groups="base.group_user"/>
            <button name="cancel" states="sourcing" string="Cancel Quotation" groups="base.group_user"/>
        </xpath>
        <xpath expr="/form/header/field[@name='state']" position="replace">
            <field name="state" widget="statusbar" statusbar_visible="draft,sourcing,sent,progress,done" statusbar_colors='{"invoice_except":"red","waiting_date":"blue"}'/>
        </xpath>
          ...

    </field>

</record>


#button methode
@api.multi
def sourcing(self):
    self.state = 'sourcing'
    if self.opportunity:
        ids = self.env['crm.case.stage'].search([("name", "=", "F.Z: Sourcing")])
        self.opportunity.stage_id = ids[0].id