Piwik trackPageView 2 different results

Question

I want to know about the trackPageView function,

There are 2 different results on the trackPageView function. The difference occurs when using a variable in the callback.

The variable is empty,

first :

_paq.push(['trackPageView','Variable']);

The Variable 's avg_time_on_page result is always 1 sec.

second :

_paq.push(['trackPageView']);

It's default, without arguments, the avg_time_on_page result is correct.

  <script type="text/javascript">
  var _paq = _paq || [];
  var pid = '<?php echo $postid;?>';
  _paq.push(['trackPageView',pid]);
  _paq.push(['trackPageView']);
  _paq.push(['trackEvent', 'arcpost', 'wsite', pid]);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u="<?php echo JSPIWIK_URL;?>";
    _paq.push(['setTrackerUrl', u+'piwik.php']);
    _paq.push(['setSiteId', <?php echo JSPIWIK_SITEID;?>]);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
    g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
  })();
</script>

default:

PAGE NAME :The boys, please... AVG. TIME ON PAGE: 55s

var: gubof1

PAGE NAME :gubof1 AVG. TIME ON PAGE: 1s

How is this possible?