Answer preceding label missing when viewing all results

We've got a questionnaire with some radio button questions and some questions of type label.

All answers that precede a question of type label are missing in results on the "View all responses" tab.

On line 341 of questionnaire.class.php, questions of type label skip the incrementation of $i, so the result of this question overwrites the result of the last question.

if ($question->type_id < QUESPAGEBREAK) {
  $i++;
}