PHP notices at admin/settings/service_links/services from form elements without #parents

On a D6 test site I'm working with, when I visit admin/settings/service_links/services I get a bunch of PHP notices like this:

notice: Undefined offset: 0 in /.../includes/form.inc on line 834.

This is inside form_get_error(). I added a little debugging code in there to print out the $element when it's having trouble, and got a bunch of entries like this:

array(13) {
 ["#parents"]=>
  array(0) {
  }
  ["#tree"]=>
  bool(false)
  ["#input"]=>
  bool(true)
  ["#return_value"]=>
  int(1)
  ["#process"]=>
  array(1) {
    [0]=>
    string(16) "form_expand_ahah"
  }
  ["#required"]=>
  bool(false)
  ["#attributes"]=>
  array(0) {
  }
  ["#value"]=>
  int(1)
  ["#id"]=>
  string(33) "edit-service-links-show-delicious"
  ["#name"]=>
  string(29) "service_links_show[delicious]"
  ["#description"]=>
  NULL
  ["#type"]=>
  string(8) "checkbox"
  ["#title"]=>
  NULL
}

I don't have time to dig deeply into theme_service_links_drag_table() and all the magic it's doing to try to figure out what's going wrong. But there's clearly a bug in there somewhere, since if I just put return drupal_render($form); at the top of the function, the notices go away (along with the draggable table, obviously). ;) My suspicion is that something about the attempt to selectively render elements is confusing form API. Generally, it gets pissy if you never finish up with the drupal_render() on the whole form. I tried a few quick things but didn't have any luck, so I'm going to ignore it for now. But I wanted to open an issue with my findings in case anyone else is having the same problems and has better luck (and more time!) to debug. ;)

Cheers,
-Derek

p.s. I'm on PHP 5.3 in case that matters...