Per documentation at http://framework.zend.com/manual/en/…

"If $content is present and not a boolean FALSE, then that content is rendered within the start and close form tags; if $content is a boolean FALSE (the default), only the opening form tag is generated."

This works fine for the standard form view helper but when Dojo is enabled $content is set to '' which prevents only the opening tag from being created. The culprit is in Zend_Dojo_View_Helper_Form.php in function form($id, $attribs = null, $content = false).

        if (false === $content) {
            $content = '';
        }