"Log Sent Mail" forgets it's value

On admin/settings/pontomail the option Log Sent Mail forgets it's value after submitting.
So I checked the form and it seems to be corrupted - in 4.7 too.

  $form['pontomail_options'] = array('#type' => 'checkbox',
    '#title' => t('Log Sent Mail'),
    '#description' => t('This will log all sent mail that is sent by all users. Users will then be
     able to view any mail they have sent through Pontomail Webmail'));

should be something like

  $form['pontomail_options']['pontomail_log_sent'] = array('#type' => 'checkbox',
    '#title' => t('Log Sent Mail'),
    '#default_value' => variable_get('pontomail_log_sent', 0),
    '#description' => t('This will log all sent mail that is sent by all users. Users will then be
     able to view any mail they have sent through Pontomail Webmail'));

But it doesn't seem to be functional anyway by now - or am I wrong here?
vg