AJAX-form replaced div comes back empty when logged out

Question

I have an AJAX form that replaces a section of itself successfully when the user is logged in. But when logged out, the demo-area section comes back with the #prefix and #suffix but no item-header or item-display. $files is an array of my objects that create the custom-themed sections successfully. I can't figure out what is causing them to return empty in AJAX when logged out.

I think permissions are fine. When logged in, the initial form load and AJAX replacements work as intended. When logged out, the demo-area loads correctly with the page, but is then replaced with only #prefix/#suffix on AJAX calls.

Here is the part of my form builder function in question:

$files = array();
foreach ($node->field_file[$node->language] as $field_file) {
  $files[] = new ClientDemoItem($field_file);
}

$form['file-index'] = array(
  '#type' => 'select',
  '#options' => array_keys($files),
  '#default_value' => 0,
  '#ajax' => array(
    'callback' => 'client_demo_load_item',
    'wrapper' => 'client-demo-area',
  ),
);

$file_index = isset($form_state['values']['file-index'])? $form_state['values']['file-index'] : 0;

$form['demo-area'] = array(
  '#prefix' => '<div id="client-demo-area">',
  'item-header' => $files[$file_index]->buildHeader(),
  'item-display' => $files[$file_index]->buildDisplay(),
  '#suffix' => '</div>',
);

Here is the simple AJAX callback:

/*
 * Replace the demo area with the requested file display
 */
function client_demo_load_item($form, $form_state) {
  return $form['demo-area'];
}

Here is what the buildHeader() function does:

  public function buildheader() {

    $item = array(
      '#theme' => 'client_demo_item_header',
      '#url' => file_create_url($this->uri),
      '#description' => $this->description,
      '#filename' => $this->filename,
      '#filesize' => filesize($path),
      '#timestamp' => $this->timestamp,
      '#fid' => $this->fid,
      '#item_file' => $this,
    );

    return $item;
  }