i'm trying to add state named sourcing to sale order quotation .. everything is good i added a button to change draft to my state named sourcing .. the problem is when i change state to sourcing my quotation become order ..

how to stay in quotation 

here is my code 

python :

class devis_stage(models.Model):
    _inherit = 'sale.order'

    state = fields.Selection(selection_add=[('sourcing', 'Sourcing')])


    @api.one
    def sourcing(self):
        self.state = 'sourcing'

view.xml:

<openerp>
    <data>

        <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>
    </data>
</openerp>

sale_workflow.xml:

   <?xml version="1.0" encoding="utf-8"?>

<openerp>
    <data>
        <record id="act_quotation_sourcing" model="workflow.activity">
            <field name="wkf_id" ref="sale.wkf_sale"/>
            <field name="name">Sourcing</field>
            <field name="kind">function</field>
            <field name="action">write({'state':'sourcing'})</field>
        </record>
        <record id="trans_quotation_draft_to_sourcing" model="workflow.transition">
            <field name="act_from" ref="sale.act_draft"/>
            <field name="act_to" ref="act_quotation_sourcing"/>
            <field name="signal">sourcing</field>
        </record>
    </data>
</openerp>