No browsernames in wp-piwik, but in piwik dashboard

In my WP-Piwik-statistics there are a circle chart and a list with numbers of visits sorted by browser. But in both are no names for the browser.

I checked with the Piwik dashboard and there are the names correctly named. Other data like display settings and OS are shown normally, only the browser names aren’t correct.

I use Chrome and tested it in Firefox, too. It doesn’t work.

It’s a bug in the plugin or a failure in my site/configuration?

http://wordpress.org/extend/plugins/wp-piwik/