IE seems to sends XMLHttpRequest as two TCP packets (see https://josephscott.org/archives/2009/08/xmlhttprequest-xhr-uses-multiple-packets-for-http-post). I could verify this for a simple request with IE11 on a win7 box using wireshark. However, this seems to confuse Sming, it will report an empty request body. The webserver seems to handle fragmented packets not correctly. A possible workaround might be to use GET instead of POST.