Titles Missing if Multiple Posts

If more than one message is in the mailhandler mailbox, only the LAST item gets a title (correctly, from the subject line). The other items get imported and nodes are created, but with no titles in them. This behavior occurs on any and every import.
The feeds importer is posted below. Feeds module ver. is 6.x-1.0-beta11.
Of course, this could be a feeds issue, but I don't know how to rule that out.
Thank you very much.

$feeds_importer = new stdClass;
$feeds_importer->disabled = FALSE; /* Edit this to true to make a default feeds_importer disabled initially */
$feeds_importer->api_version = 1;
$feeds_importer->id = 'blog_posts';
$feeds_importer->config = array(
  'name' => 'Blog Posts',
  'description' => 'Import email posts, via mailhandler',
  'fetcher' => array(
    'plugin_key' => 'MailhandlerFetcher',
    'config' => array(
      'filter' => 'MailhandlerFiltersNodes',
    ),
  ),
  'parser' => array(
    'plugin_key' => 'MailhandlerParser',
    'config' => array(
      'default_commands' => 'status: 0',
      'commands_failed_auth' => 'status: 0',
      'available_commands' => 'status',
      'command_plugin' => array(
        'MailhandlerCommandsHeaders' => 'MailhandlerCommandsHeaders',
        'MailhandlerCommandsDefault' => 'MailhandlerCommandsDefault',
        'MailhandlerCommandsFiles' => 'MailhandlerCommandsFiles',
      ),
      'authenticate_plugin' => 'MailhandlerAuthenticateDefault',
    ),
  ),
  'processor' => array(
    'plugin_key' => 'FeedsNodeProcessor',
    'config' => array(
      'content_type' => 'blog',
      'input_format' => '2',
      'update_existing' => '0',
      'expire' => '-1',
      'mappings' => array(
        0 => array(
          'source' => 'subject',
          'target' => 'title',
          'unique' => FALSE,
        ),
        1 => array(
          'source' => 'body_text',
          'target' => 'body',
          'unique' => FALSE,
        ),
      ),
      'author' => '3',
      'authorize' => 0,
    ),
  ),
  'content_type' => '',
  'update' => 0,
  'import_period' => '0',
  'expire_period' => 3600,
  'import_on_create' => 1,
);