Why do I have "HTTP 400 bad request" during HTTP POST requests to a Webservices on EAP ?

Issue

We are getting HTTP 400 bad request, Connection Closed error during HTTP POST. The error occurs on JBOSS EAP 6.1 environment.
In the access log:

2815    2013-12-05 19:53:33.417004  192.168.0.1 192.168.0.2 HTTP    210 HTTP/1.1 400 Bad Request 

We can reproduce the error consistently. We had prior 120 successive calls, each call invokes a web service. The web service calls fail after 107 successive call to same web service method.