MW 1.27, HHVM 3.14.3.
Warnings in /var/hhvm/error.log on every request:
\nWarning: header() expects parameter 3 to be integer, null given in /var/www/wiki/w/includes/WebResponse.php on line 42
Which is worse, this bug also breaks saving at least some of the pages. However, it is enough to replace
header( $string, $replace, $http_response_code );
with
if ($http_response_code) {
header( $string, $replace, $http_response_code );
} else {
header( $string, $replace );
}in line 42 of includes/WebResponse.php (method WebResponse::header( $string, $replace = true, $http_response_code = null )) to fix it.