NGINX + HHVM + SOAP Chunked response - php

Question

Seems that NGINX wont pass the correct HTTP protocol to HHVM backend.
Here the tests I've done:
If the client send a HTTP/1.1 request (non chunked) NGINX pass it to the HHVM backend and the correct response come back to the client
(client) (server backend)
HTTP/1.1(non chunked) -> NGINX -> HHVM
|
v
(HTTP/1.1 200) <- NGINX <- (non chunked response)
If the client send a HTTP/1.1 request (chuncked), the server produce a chunked reponse, but NGINX fire this log message
upstream prematurely closed connection while reading response header from upstream, request: "POST /soap HTTP/1.1", upstream: "fastcgi://unix:/var/run/hhvm/sock:"
and return a 502 (bad gateway) response
(client) (server backend)
HTTP/1.1(chunked) -> NGINX -> HHVM
|
v
(HTTP/1.1 502) <- NGINX <- (chunked response)
Why I got a 502 from NGINX using chunked response?
Is there something wrong with hhvm/fastcgi/hhvm config?
I double checked that backend give a correct 1/1 response :(
I've a scenario with:
NGINX:nginx/1.4.6 (Ubuntu)
HHVM: HipHop VM 3.6.1 (rel)
The NGINX config is
server {
listen 80;
server_name xxxxx;
root /usr/share/nginx/web;
include hhvm.conf;
location / {
# try to serve file directly, fallback to rewrite
try_files $uri #rewriteapp;
}
location #rewriteapp {
# rewrite all to app.php
rewrite ^(.*)$ /app.php/$1 last;
}
location ~ ^/(app|app_dev|app_benchmark|app_logall|config)\.php(/|$) {
fastcgi_keep_conn on;
#fastcgi_pass 127.0.0.1:9000;
fastcgi_pass unix:/var/run/hhvm/sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_buffer_size 128k;
fastcgi_buffers 256 16k;
fastcgi_busy_buffers_size 256k;
fastcgi_temp_file_write_size 256k;
fastcgi_read_timeout 240;
fastcgi_intercept_errors on;
include fastcgi_params;
}
}