When I have Piwik running on my site, the link above opens in the same window and not in a new window. When I disable Piwik (e.g by shutting down the piwik server) the above links opens in a new window.
However this always works for external links (e.g. linking to a different site), regardless if Piwik is running or not.
While trying to create a simple HTML file I discovered the reason for the problem.
We are using the Javascript framework “Alloy UI”. The links mentioned above were created using this framework. Somehow the “Alloy UI” framework adds an “onclick”-Handler to the link. Deep inside the event handler I found a call to “event.preventDefault()”. When I remove this line from the event handler, everything works fine.
So this seems to be a problem of “Alloy UI” and not a Piwik problem.