an request body might not be passed to backend,
the bug was introduced in r1212

src/core/ngx_output_chain.c

diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index e2dcc4c..cc635c9 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -489,10 +489,10 @@
 
     if (ctx->out == NULL) {
         ctx->last = &ctx->out;
-    }
 
-    if (!ctx->connection->buffered) {
-        return NGX_OK;
+        if (!ctx->connection->buffered) {
+            return NGX_OK;
+        }
     }
 
     return NGX_AGAIN;