Notice: Undefined index: #field_name in files_undo_remove_file_process() (line 41 of modules/files_undo_remove/files_undo_remove

After uploading a File to a theme-settings field:
admin/appearance/settings/%theme

With a Field Something Like this:

 $form['background'] = array(
    '#type' => 'managed_file',
    '#title' => t('Background Image'),
    '#default_value' => theme_get_setting('background'),
  );

If Files undo remove is enabled, uploading a File to a managed_file field that is a standard field and not attached to an entity, will result in this Error:

Notice: Undefined index: #field_name in files_undo_remove_file_process() (line 41 of modules/files_undo_remove/files_undo_remove.module).

thanks!
david