Delay on nginx serving from backend

Dear Nginx community ,

I am running nginx 1.04 , ( also tried 1.0 ) , and the backend has an
ejabber server serving http requests.

I am experiencing delays in requests being served when i serve the
request via nginx , whereas serving the same request from the backend
works without any delay .

On debugging , i can see that nginx received a response from backend
within milliseconds but is not serving back the user with the response .
there is a 5 second delay at this point . please find below the debug
log just before and after the delay .

Debug Log is pasted here nginx_delay - Pastebin.com

Notice that there is no activity between
06:26:33 and 06:26:38

Can anyone explain what could cause this delay .

There is no network connectivity issue between nginx and upstream , as
from the same machine when i connect directly to the backned result is
received instantly .

I should be seeing a 400 request right away , but it takes 5-6 seconds
for the request to come .

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