diff -r 0ebf6344db81 src/http/modules/ngx_http_proxy_module.c
--- a/src/http/modules/ngx_http_proxy_module.c	Fri Apr 26 11:11:03 2013 +0800
+++ b/src/http/modules/ngx_http_proxy_module.c	Fri May 03 10:52:41 2013 +0800
@@ -615,7 +615,8 @@
 #endif
 
     { ngx_string("proxy_internal_body_length"), NULL,
-      ngx_http_proxy_internal_body_length_variable, 0, NGX_HTTP_VAR_NOHASH, 0 },
+      ngx_http_proxy_internal_body_length_variable, 0,
+      NGX_HTTP_VAR_NOCACHEABLE|NGX_HTTP_VAR_NOHASH, 0 },
 
     { ngx_null_string, NULL, NULL, 0, 0, 0 }
 };