in kernel/classes/ezurlwildcard.php, we can find this:

        $cacheFile = eZClusterFileHandler::instance( $info['path'] . "_index.php" );

        if ( !$cacheFile->exists() )
            return false;

        $fetchedFilePath = $cacheFile->fetchUnique();
        include_once( $fetchedFilePath );
        $cacheFile->fileDeleteLocal( $fetchedFilePath );

It means that everytime this file is loaded, it is copied as a unique file, its contents included, and the locally fetched unique file is removed... unless there was a valid reason why this was implement this way, it should be changed to the standard way of loading caches.