Timeout when sending over 16k of data with UTF-8 characters

[Bryan McLellan]

I'm experiencing an issue where nginx and having a difficult time
determining the cause. It is timing out on an HTTPS PUT (to an HTTP
backend) when content length is greater than 16384 (per
$content_length) and it contains UTF-8 characters. The connection
hangs and I get a 408 returned by nginx after 60 seconds. When I make
the same call directly to the backend, it succeeds. Removing the UTF-8
characters or reducing the seize to 16384 or below will both allow the
request to succeed through nginx.

client_body_buffer_size is defaulting to 8k, and using
$request_body_file I've determined that it isn't the use of a
temporary file triggering the error. Are there any other configuration
values that default to 16k?

My current nginx configuration:
nginx: nginx version: nginx/1.0.5
nginx: built by gcc 4.4.3 (Ubuntu 4.4.3-4ubuntu5)
nginx: TLS SNI support enabled
nginx: configure arguments: --conf-path=/etc/nginx
--prefix=/srv/nginx/1.0.5 --with-http_ssl_module
--with-http_stub_status_module --add-module=../nginx-x-rid-header
--with-ld-opt=-luuid

I also tried 1.1.6 to see if its UTF-8 patch would help, to no avail:
nginx: nginx version: nginx/1.1.6
nginx: built by gcc 4.4.3 (Ubuntu 4.4.3-4ubuntu5)
nginx: TLS SNI support enabled
nginx: configure arguments: --conf-path=/etc/nginx
--prefix=/tmp/nginx-1.1.6 --with-http_ssl_module
--with-http_stub_status_module --add-module=../nginx-x-rid-header
--with-ld-opt=-luuid

Successful PUT:

$status 200
$request_time 0.943
$body_bytes_sent 16384
$upstream_status 200
$upstream_response_time 0.216
$request_length 17330
$content_length 16384
$request_body_file /srv/nginx/1.0.5/client_body_temp/0000000249

Failing PUT:
$status 408
$request_time 60.911
$body_bytes_sent -
$upstream_status -
$upstream_response_time -
$request_length 17330
$content_length 16385
$request_body_file /srv/nginx/1.0.5/client_body_temp/0000000250

Ideas?
Bryan