Just an update...
I've been able to reproduce this issue locally. There is a bug in the version of Netty that we are using which will cause the xhr_streaming protocol to fail due to invalid chunks being sent:

git show b669237bac0027ab039da0931ec3dc13fb223b3e
commit b669237bac0027ab039da0931ec3dc13fb223b3e
Author: Derek Troy-West <derek@troywest.com>
Date:   Tue Aug 27 18:36:59 2013 +1000

    HTTP Chunk, wrong delimiter written

diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java b/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java
index 3819a15..1bf24bf 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java
@@ -45,7 +45,7 @@ public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageTo
     private static final byte[] ZERO_CRLF = { '0', CR, LF };
     private static final byte[] ZERO_CRLF_CRLF = { '0', CR, LF, CR, LF };
     private static final byte[] HEADER_SEPARATOR = { COLON, SP };
-    private static final ByteBuf CRLF_BUF = unreleasableBuffer(directBuffer(ZERO_CRLF.length).writeBytes(ZERO_CRLF));
+    private static final ByteBuf CRLF_BUF = unreleasableBuffer(directBuffer(CRLF.length).writeBytes(CRLF));
     private static final ByteBuf ZERO_CRLF_CRLF_BUF = unreleasableBuffer(directBuffer(ZERO_CRLF_CRLF.length)
             .writeBytes(ZERO_CRLF_CRLF));

With the above fix I'm able to reproduce this issue and will continue investigating.

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