There is an error when using second and third page of calculated question editing as there is no tags on theses pages.
So question.php line 208
if (!empty($CFG->usetags))

{ require_once($CFG->dirroot.'/tag/lib.php'); tag_set('question', $question->id, $fromform->tags); }
should be changed to

if (!empty($CFG->usetags) && isset($fromform->tags)) { require_once($CFG->dirroot.'/tag/lib.php'); tag_set('question', $question->id, $fromform->tags); }

I will CVs the correction in the next days (back to work tuesday).