ZF-3339: DtDdWrapper is not xhtml valid for radio buttons
The empty definition term which is placed using Zend_Form when radio buttons are being generated is not XHTML valid. Therefore I suggest that, if the doctype is set to XHTML, the wrapper either doesn't place the empty definition term, or places a nonbraking space inside it . This has been fixed if no label is set (http://framework.zend.com/issues/browse/ZF-2989) but appearantly radio buttons use different 'label generation' by default. I think this is also the case with checkboxes.