30% conversions missing !! (no replies)

Hello,

I have a BIG issue with my tracking : I'm tracking goals in my website. I've been testing my tracker, and the tracker tracks correctly the goals.
If I go on a tracked page and press F5, I can see it correctly tracked the pageview and conversion on Piwik. I did this procedure 10 times in a row with no issue, F5, check, F5, check..
However, if I press F5 (and I wait for the page to be load) about 30 times, then I check on Piwik if everything is tracked correctly, I see that the 30 pageviews have been tracked fine, but I get about ~~22-24 conversion everytime. I searched for a huge number of possibilities, but I didn't find the solution.
To do those tests, I did use a private page without anything loading on it, just the javascript tracker, and on a database unused by anything but this page, so it's not a problem of 2 many requests or something like that. I checked my apache logs, vhost logs etc.. without success (indeed, visits are correct but I'm just missing goals)

It is live on some websites of my own and I compared stats with GA's, and visits count is correct, but conversions count of Piwik is missing 30% of GA's. (That's how I noticed the issue)

Do you have any ideas? I'm quite desperate..

Here is my tracking JS code if it can help

<script type="text/javascript">
  var _paq = _paq || [];
  _paq.push(['trackGoal', 2]);
  _paq.push(['setTrackerUrl','[..]/piwik.php']);
  _paq.push(['setSiteId', '7']);
  _paq.push(['enableLinkTracking']);
  _paq.push(['trackPageView']);
</script>

<script type="text/javascript" src="[..]/piwik.js"></script>