about proxy_request_buffering (no replies)

Hello.

Though I'm trying to apply 'proxy_request_buffering off;' for unbuffered uploading,
The buffering still seems to be enabled from error.log.

# nginx.conf

server {
listen 443 ssl spdy;
server_name example.com;

location /upload {
proxy_request_buffering off;
proxy_pass http://upload_backend;
}
}

# error.log

2015/03/29 14:02:20 [warn] 6965#0: *1 a client request body is buffered to a temporary file /etc/nginx/client_body_temp/0000000001, client: x.x.x.x, server: example.com, request: "POST /upload HTTP/1.1", host: "example.com"


The warning above is not output when SPDY is not enabled.


Is proxy_request_buffering always enabled when SPDY is enabled?