When elements belong to a DisplayGroup and the form has specified an elementsBelongTo setting, the setting is not being used to determine the element name and id correctly. For instance:

$form->addElements(array(
    new Zend_Form_Element_Text('foo'),
    new Zend_Form_Element_Text('bar'),
    new Zend_Form_Element_Text('baz'),
    new Zend_Form_Element_Text('bat'),
));
$form->addDisplayGroup(array('bar', 'baz'), 'barbaz');
$form->setElementsBelongTo('myform');

When the form is rendered, all elements should have a name of 'myform[]' and an id of 'myform-'. However, the elements inside the display group do not.