Plesk is shipping their own out-dated build of Nginx 1.6.0 (package sw-nginx). Several important bug fixes and security fixes have been released in updates 1.6.1, 1.6.2 and 1.6.3. See http://nginx.org/en/CHANGES-1.6
Please update the Nginx package that is shipped with Plesk.
Please update the Nginx package that is shipped with Plesk.