I also had the same mistakes of double request
I try to do proxy_ignore_client_abort on，http_499 fewer errors, but appeared http_400 error.
the double request at the some time problem still was not solved

sever info
nginx (gzip)--（static request）-->squid--->apache
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(php request )
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nginx(loadbalance+gzip)
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apache

I have 1 Loadbalancer with nginx and 4 servers with apache.
apache 2.0.59

nginx version: nginx/0.7.65
built by gcc 4.1.2 20080704 (Red Hat 4.1.2-44)
configure arguments: --user=www --group=www --prefix=/usr/local/nginx/ --with-http_stub_status_module --with-http_realip_module