getFormField multi elements if element does not have an id

I've found and issue while trying to tick a checkbox created by Zend Framework 2, using its Multicheckbox element. It produces n input fields all with the same name foo[], and there isn't an easy way to set an id for each of them. When I try to tick one or more of these elements both  the $element->getAttribute('id') and the $fieldNode->getAttribute('id') methods return the same empty string. As a result, only the last checkbox is checked. Applying the comparison to the value instead of the id when it is not present, checkboxes work properly.