TrackEvent won't work but gives Status 200 - Piwik 2.4.1



Is it possible to track multiple buttons with the same “onclick” parameter?
The code is automatically generated and looks like this:

<a href="#" onclick="javascript:_paq.push(['trackEvent', 'Merkzettel', 'MZ_wnd']);">Zum Merkzettel</a>

I’ve got 8 from those onClick-Parameter on the same page.

When clicked, the browser returns a Status 200 for both requests, but Piwik won’t show any data!

Could someone help me?
Many thanks in advance!

Piwik Version 2.4.1.