TableSort extender sorts with the wrong column when the column title contains spaces

It seems like TableSort extender fails to recognize correctly the column to sort on when the column title contains spaces. e.g. consider the following $headers section:

  $headers = array(
      array(
          'data' => t('Type'),
          'field' => 'd.type',
          'class' => array('search-result-header col-type')),
      array(
          'data' => t('Title'),
          'field' => 'title',
          'sort' => 'asc',
          'class' => array('search-result-header col-title')),
      array(
          'data' => t('Author'),
          'field' => 'author',
          'class' => array('search-result-header col-author')),
      array(
          'data' => t('Year of Publication'),
          'field' => 'publish_year',
          'class' => array('search-result-header col-publish-year')),
      array(
          'data' => t('Keywords'),
          'class' => array('search-result-header col-keywords')),
      array(
          'data' => '',
          'class' => array('search-result-header col-download')));

The link for "Year of Publishing" header is generated as:
/drupal/?q=document&sort=asc&order=Year%20of%20Publication

But clicking on that link any number of times always sorts in ascending order by the "Title" column. If I remove spaces from "Year of Publishing" header, it starts working fine.