This is the beginning of taxonomy_form_term_submit function:

function taxonomy_form_term_submit($form, &$form_state) {
  if ($form_state['triggering_element']['#value'] == t('Delete')) {
    // Execute the term deletion.
    if ($form_state['values']['delete'] === TRUE) {
      return taxonomy_term_confirm_delete_submit($form, $form_state);
    }
    // Rebuild the form to confirm term deletion.
    $form_state['rebuild'] = TRUE;
    $form_state['confirm_delete'] = TRUE;
    return;
  }

I've never seen such logic anywhere in Drupal or contrib modules. I thik it's quite safe to say this should be removed and custom page should be created with confirm_form for taxonomy term deletion.