I have inherit this  Settings-> Configuration -> Accounting. I have added one check box. when i mark this check box to true, after click on "apply" button, this check box showing like uncheked check box. But the value storing in database is "True".

.py file.

class account_config_settings_extension(osv.osv):
    _inherit = "account.config.settings"
    _columns = {
    'threelevelinvoiceapproval': fields.boolean('Three level checking for invoices'),
    }
    _defaults = {
        'threelevelinvoiceapproval':False
         }

.xml record:

<record id="account_config_settings_extension_form" model="ir.ui.view">
        <field name="name">account.config.settings.form</field>
        <field name="model">account.config.settings</field>
        <field name="type">form</field>
        <field name="inherit_id" ref="account.view_account_config_settings"/>
        <field name="arch" type="xml">
            <field name="default_sale_tax" position="after">  
                <br></br>
                <field name="threelevelinvoiceapproval"/>
                <label for="threelevelinvoiceapproval"/>
            </field>
        </field>
    </record>

I have tried without _defaults{ } also... but it's always showing uncheck check box, irrespective of the database value. Please tell me how can i overcome this problem?