nginx silently drops response body of POST depending on its length

[zildjohn01]

I've come across an incredibly weird problem with POST responses using
nginx 1.0.1 and uWSGI 0.9.7.2 on CentOS 5.6.

uWSGI successfully sends the response body to nginx, but nginx seems to
ignore it if both (1) the request method is POST, and (2) the response
length is less than 4052 bytes. The issue doesn't occur when serving
directly using `uwsgi --http`, so I'm pretty sure the problem is
something to do with nginx.

To explain things in code, this Python results in the desired response:

....def app_uwsgi(environ, start_response):
........start_response('200 OK', [('Content-type', 'text/html')])
........return [b'x' * 4052]

while this results in zero bytes being sent to the client for POST
requests:

....def app_uwsgi(environ, start_response):
........start_response('200 OK', [('Content-type', 'text/html')])
........return [b'x' * 4051]

I stripped down to a minimal nginx.conf, and the issue still occurs:

....events {
........worker_connections  1024;
....}

....http {
........upstream uwsgi_connect {
............server  127.0.0.1:39275;
........}

........server {
............listen       20101;
............server_name  domain.net;

............location / {
................uwsgi_pass  uwsgi_connect;
................include     uwsgi_params;
............}
........}
....}

Does anyone have any clue what could be causing this behavior?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,196581,196581#msg-196581