CXF Web Service with activated MTOM always creates multipart message

Issue

• multipart/related messages exchanged for @MTOM annotated endpoint even if no attachment is included
• Java class with @WebService annotation and also @MTOM (enabled =true) has two methods with @WebMethod annotation: one returns binary data , the other does not.
  When calling the second method i.e. with soapui, the raw data returned is multi-parted even though it is not required

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Type: multipart/related; type="application/xop+xml"; boundary="--uuid:febe2942-996f-4c83-a4ec..."; start="<root.message@cxf.apache.org>"; start-info="application/soap+xml"
Content-Length: 574
Date: Tue, 20 Sep 2016 12:43:09 GMT

----uuid:febe2942-996f-4c83-a4ec.....
Content-Type: application/xop+xml; charset=UTF-8; type="application/soap+xml"
Content-Transfer-Encoding: binary
Content-ID: <root.message@cxf.apache.org>

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
     <env:Header xmlns:env="http://www.w3.org/2003/05/soap-envelope"></env:Header>
    <soap:Body>
       <ns2:noBlobResponse xmlns:ns2="http://ws.example.com/framework/wstest/MTOMTestWS"><String>Da is' was :-) : Hallo</String></ns2:noBlobResponse>   
    </soap:Body>
</soap:Envelope>
----uuid:febe2942-996f-4c83-a4ec...--

With JBoss EAP 5, the message was not multi-part in this situation.