I was having this same problem. It looks like some debugging code was accidentally left in this release. If you’re comfortable fixing it yourself, you can edit the wp-to-buffer.php file. Make lines 197-201 look like this:
// Do some logging for debugging
//$fp = fopen('/Users/tim/sites/_logs/log.txt', 'w+');
//fwrite($fp, print_r($defaults,true));
//fwrite($fp, print_r($post,true));
//fclose($fp);