I want to override the "Reverse" button of stock picking to be only visible to stock.group_stock_manager.

I have used the same method as usual to override buttons:

<?xml version="1.0" encoding="utf-8"?>
<openerp>
  <data>
    <record id="view_picking_form_extend" model="ir.ui.view">
      <field name="name">stock.picking.form.extend</field>
      <field name="model">stock.picking</field>
      <field name="inherit_id" ref="stock.view_picking_form"/>
      <field name="arch" type="xml">
	<xpath expr="/form/header/button[@name='%(act_stock_return_picking)d']" position="replace">
	  <button name="%(act_stock_return_picking)d" string="Reverse" states="done" type="action" groups="stock.group_stock_manager"/>
	</xpath>
      </field>
    </record>
  </data>
</openerp>

But I get an error. It says the element cannot be located in parent view.

I have this in parent view:

<button name="%(act_stock_return_picking)d" string="Reverse" states="done" type="action" groups="base.group_user"/>

Note: If I override other button (without the '%' and 'd' characters) it works fine.

What am I doing wrong?