i attache here my "debug_http" log - note that "http finalize request" is called twice (i think that one of them nulls the connection so nulls its log too), and thats NOT happening when NOT using proxy_ignore_client_abort:

btw: i use proxy http version 1.1, if it helps

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2013/03/14 17:49:23 [info] 29550#0: *55 client prematurely closed connection while sending request to upstream, client: 10.0.0.18, server: www.aaa.com, request: "GET / HTTP/1.0", upstream: "http://x.x.x.x:80/", host: "aaa.com"
2013/03/14 17:49:23 [debug] 29550#0: *55 http finalize request: 0, "/?" a:1, c:1
2013/03/14 17:49:23 [debug] 29550#0: *55 http terminate request count:1
2013/03/14 17:49:23 [debug] 29550#0: *55 cleanup http upstream request: "/"
2013/03/14 17:49:23 [debug] 29550#0: *55 finalize http upstream request: -4
2013/03/14 17:49:23 [debug] 29550#0: *55 finalize http proxy request
2013/03/14 17:49:23 [debug] 29550#0: *55 free keepalive peer
2013/03/14 17:49:23 [debug] 29550#0: *55 free rr peer 3 0
2013/03/14 17:49:23 [debug] 29550#0: *55 close http upstream connection: 25
2013/03/14 17:49:23 [debug] 29550#0: *55 http finalize request: -4, "/?" a:1, c:1
2013/03/14 17:49:23 [debug] 29550#0: *55 http lingering close handler
2013/03/14 17:49:23 [debug] 29550#0: *55 lingering read: 0
2013/03/14 17:49:23 [debug] 29550#0: *55 http request count:1 blk:0
2013/03/14 17:49:23 [debug] 29550#0: *55 http close request
2013/03/14 17:49:23 [debug] 29550#0: *55 http log handler
2013/03/14 17:49:23 [debug] 29550#0: *55 close http connection: 23
-------------------------------