Request_completion variable and zero length 200 response

Hello,

We are using request_completion core variable to log every request.
Until
recently, we found that some requests got logged with:

$request_completion = NULL
$statue = 200
$bytes_send = 0
$body_bytes_send = 0

so the question is in what condition, will nginx set request_completion
to
NULL while at the sam time set status to 200 with zero bytes send? Is
this a
client-side problem or nginx’s bug?

Below is a sample log(request_completion is the last field and it’s
NULL):
[27/Aug/2010:18:15:43 +0800] 114.139.50.115 GET /LoginFrame.asp
61.172.242.15:80 [Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;
SV1;
GTB6.5; .NET CLR 1.1.4322)] HTTP/1.1 200 0 0