Is it possible your nginx config is tracking the js via fast-cgi instead of nginx directly?
http://www.nodroidsallowed.com/2009/08/11/update-on-nginx-and-piwik/
Also did you have to change any piwik folder permissions on v 1.10.1 that in later versions were slightly different?
http://www.nodroidsallowed.com/2009/08/11/update-on-nginx-and-piwik/
Also did you have to change any piwik folder permissions on v 1.10.1 that in later versions were slightly different?