Web api 2.1 does not work with a chunked request

I have a application running correctly on web api 2.0 platform.

When I upgrade web api to version 2.1, it does not work.

The client request code such as :

HttpWebRequest hRqst = (HttpWebRequest)WebRequest.Create("http://localhost:7897/api/Test");

hRqst.Method = "Post";

hRqst.ContentType = "application/json";

hRqst.SendChunked = true; // The key code of the problem.

Web api 2.1 would not deserialize the json content, it will deserialize the json data as a null object.