If you have a display group within a sub form, the elements contained by the display group do not get namespaced within the rendered form correctly, which leads to issues during form submission.

For example:

$subForm = new Zend_Form_SubForm();
$subForm->setLegend('Attributes');

$subForm->addElement('text', 'foo')
        ->addElement('text', 'bar')
        ->addDisplayGroup(array('foo', 'bar'), 'foobar');

$form = new Zend_Form();
$form->addSubForm($subForm, 'attributes');
echo $form->render(new Zend_View());

One would expect the following HTML:

But the following is actually received: