Nginx returning 414 even when large_client_header_buffers is set

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My nginx server needs a request whose URI is about 4k long, it currently
returns 414 with message Request-URI Too Long.

I looked online and added:

large_client_header_buffers 4 16k;

to the http block in nginx.conf, restarted nginx, still returns 414. 

I also tried to add client_header_buffer_size and set to 16k and well
but didn't help.

I have nginx 1.0.12 and built with the following options:

  "--with-http_ssl_module",
  "--with-http_gzip_static_module",
  "--add-module=../git/nginx-x-rid-header",
  "--with-ld-opt=-luuid",
  "--with-http_stub_status_module"

Anybody has any insights on the 414 problem?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,225093,225093#msg-225093