stars not showing partially

Is it supposed to? I'd like to know this as well.

I managed to solve this doing the following (in a custom module):

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Add possibility to see .5 star
 * 
 */
function rating_helper_form_fivestar_custom_widget_alter(&$form, &$form_state, $form_id) {
  drupal_add_js(array('fivestar' => array('average' => $form['vote']['#values']['average'])), array('type' => 'setting')); 
  drupal_add_js(drupal_get_path('module', 'rating_helper').'/rating_helper.js', 'file');
}

Then in the rating_helper.js:

(function ($) {
  jQuery(document).ready(function($) {   
    var $container = $('.fivestar-widget');

    // allow half stars for average
    if (typeof(Drupal.settings.fivestar.average) !== 'undefined') {
      var average = Drupal.settings.fivestar.average; // on 100
      average = average * $('.fivestar-widget .star').length /  100 ;  // against # of stars, 
      // fake doubling the number of stars to know if we should round to half or not
      average = Math.round(average * 2);
      
      if ( average % 2 == 1) {
        $container.find('.star').eq(Math.floor(average/2)).addClass('half');
      }
      
    }
  });
})(jQuery);

And then I needed to create a fourth "half star" in my template and update the css (there is probably a possibility to display only half a star from a complete star image in css, but I couldn't make it work)

.fivestar-YOURWIDGET div.fivestar-widget div.hover a,
.fivestar-YOURWIDGET div.rating div a:hover {
  background-image: url(star.png);
  background-position: 0 -32px !important;
}

div.fivestar-widget .star.on.half a{
  background-position: 0 -48px;
}