zend framework subform isValidPartial?

I have a form with several subforms on it. I have an isValid method for the form where I check if only one particular subform is valid. For example, I must check if subform2 validates properly. If subform validates, the whole form should be validated successfully, even if other subforms have wrong values. They just should not be validated. I tried something like this:

if($subform->isValidPartial($_POST))
    return true;
}else{
    return false;
}

But with no succes. This code always returns true. When the whole form is validated normally without the isValid overriden, subforms are validated properly, but thye are all validated.

isSubFormValid will return true if at least one subform is valid. You can specify subform name or pass null.

class My_Form extends Zend_Form
{
    public function isSubFormValid($name = null, array $data = null)
    {
        if (is_null($name)) {
            $subForms = $this->getSubForms();
        } else {
            $subForms = array($this->getSubForm($name));
        }

        foreach ($subForms as $subForm) {
            if ($subForm->isValid($data)) {
                return true;
            }
        }    

        return false;
    }    
}

Usage example:

class Example extends My_Form
{
    public function init()
    {
        $subForm1 = new Zend_Form_SubForm();
        $subForm1->addElement($this
            ->createElement('text', 'name')
            ->setRequired(true));

        $subForm2 = new Zend_Form_SubForm();
        $subForm2->addElement($this
            ->createElement('text', 'name')
            ->setRequired(true));

        $this->addSubForm($subForm1, 'form1');
        $this->addSubForm($subForm2, 'form2');

        $this->addElement($this->createElement('submit', 'send'));
    }    
}

/* ... */
public function indexAction()
{
     $form = new Example();

     if ($this->_request->isPost()) {
         if ($form->isSubFormValid(null, $this->_request->getPost())) {
             die('is valid');
         }
     }

     $this->view->form = $form;
}

/* ... */