Периодические проблемы с fastc gi, неполный/пустой ответ от fastcgi ph p backend

[Noon es Shadow <noonesshadow@xxxxxxxxx>]

Схема:
Клиент посылает запрос, если это динамика то Нгинк пересылает запрос на бэкенд php по fastcgi, тип ответа text/xml, и выполняет трансформацию по заданному шаблону XSL
Изредка, примерно раз из 100, случается следующее:
Клиенту выдается ошибка 500 (internal server error), в лог пишется
not well formed XML document while sending to client
При повторном обновлении страницы все срабатывает как надо.

Система: Linux 2.6.25-14.fc9.i686, epoll,

configure arguments: --with-http_xslt_module --without-http_rewrite_module --without-http_memcached_module --without-http_upstream_ip_hash_module --with-debug --with-pcre=./pcre-7.9
(аналогично происходит и при configure arguments: --with-http_xslt_module --with-pcre=./pcre-7.9)

--with-debug:
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream request: "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream dummy handler
2009/06/05 12:30:46 [debug] 17496#0: timer delta: 1
2009/06/05 12:30:46 [debug] 17496#0: posted events 00000000
2009/06/05 12:30:46 [debug] 17496#0: worker cycle
2009/06/05 12:30:46 [debug] 17496#0: epoll timer: 52840
2009/06/05 12:30:46 [debug] 17496#0: epoll: fd:18 ev:0005 d:09A082C1
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream request: "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream process upstream
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe read upstream: 1
2009/06/05 12:30:46 [debug] 17496#0: *5 readv: 5:4096
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe recv chain: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe buf free s:0 t:1 f:0 09A39F78, pos 09A39F78, size: 1616 file: 0, size: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe buf free s:0 t:1 f:0 09A3CF90, pos 09A3CF90, size: 0 file: 0, size: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe buf free s:0 t:1 f:0 09A3AF80, pos 09A3AF80, size: 0 file: 0, size: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe buf free s:0 t:1 f:0 09A37F68, pos 09A37F68, size: 0 file: 0, size: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe buf free s:0 t:1 f:0 09A38F70, pos 09A38F70, size: 0 file: 0, size: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 input buf #5 09A39F78
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 01
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 06
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 01
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 01
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 07
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record length: 1
2009/06/05 12:30:46 [debug] 17496#0: *5 input buf #5 09A3A5B0
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 01
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 03
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 01
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 08
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record byte: 00
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi record length: 8
2009/06/05 12:30:46 [debug] 17496#0: *5 http fastcgi sent end request
2009/06/05 12:30:46 [debug] 17496#0: *5 input buf 09A3A5B0 1
2009/06/05 12:30:46 [debug] 17496#0: *5 free: 09A3CF90
2009/06/05 12:30:46 [debug] 17496#0: *5 free: 09A3AF80
2009/06/05 12:30:46 [debug] 17496#0: *5 free: 09A37F68
2009/06/05 12:30:46 [debug] 17496#0: *5 free: 09A38F70
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe write downstream: 1
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe write downstream flush in
2009/06/05 12:30:46 [debug] 17496#0: *5 http output filter "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 copy filter: "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 xslt filter body
2009/06/05 12:30:46 [debug] 17496#0: *5 copy filter: 0 "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 pipe write downstream done
2009/06/05 12:30:46 [debug] 17496#0: *5 event timer: 18, old: 2948757598, new: 2948757635
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream exit: 00000000
2009/06/05 12:30:46 [debug] 17496#0: *5 finalize http upstream request: 0
2009/06/05 12:30:46 [debug] 17496#0: *5 finalize http fastcgi request
2009/06/05 12:30:46 [debug] 17496#0: *5 free rr peer 1 0
2009/06/05 12:30:46 [debug] 17496#0: *5 close http upstream connection: 18
2009/06/05 12:30:46 [debug] 17496#0: *5 event timer del: 18: 2948757598
2009/06/05 12:30:46 [debug] 17496#0: *5 http upstream temp fd: -1
2009/06/05 12:30:46 [debug] 17496#0: *5 http output filter "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 copy filter: "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 xslt filter body
2009/06/05 12:30:46 [error] 17496#0: *5 not well formed XML document while sending to client, client: ***.***.***.***, server: ***.***.***.***, request: "GET /info/s32.html HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "***.***.***.***"
2009/06/05 12:30:46 [debug] 17496#0: *5 http special response: 500, "/info/s32.html?"
2009/06/05 12:30:46 [debug] 17496#0: *5 http set discard body
2009/06/05 12:30:46 [debug] 17496#0: *5 xslt filter header
2009/06/05 12:30:46 [debug] 17496#0: *5 HTTP/1.1 500 Internal Server Error