Calling addTracker twice causes JS-Error and no Tracking

we want to track to three different Websites:
The first (as usual) with _paq.push(['setSiteId','1']); and the second with _paq.push(['addTracker', u+'piwik.php', '2']);. 'Till this point everything works fine: Both Websites get’s data.
But if we add a third tracker (with a second addTracker) _paq.push(['addTracker', u+'piwik.php', '3']); only the primary Website is tracked.

In the JS-Console the error
The method addTracker is registered more than once in "_paq" variable. Only the last call has an effect. Please have a look at the multiple Piwik trackers documentation:
is shown. The documentation doesn’t say anything about a limitation to two trackers and it implies that more trackers are supported.

A strange behavior is, that sometimes the tracking works, especially if we have the developer-Tools (F12) open.
Our environment:

  • Browser: IE11;
  • Piwik: 3.0.2;
  • MySQL: 5.5.54;
  • PHP: 7.0.15

Is there any solution to track to three different Websites?
Thank you in advance

Hello, we document this case in: JavaScript Tracking Client: Integrate - Piwik Analytics - Developer Docs - v3