Mock Response Step doesn't work when using WS-A addressing

If I have a project that makes a callout to an external service, the mock response step doesn't appear to work. I can set up a Mock Service and run that, which will capture requests coming in, but when turning that off and using only the Mock Response Step, nothing happens and the service is not invoked. This is difficult to test Asynchronous Web services with callback operations.

From the service making the Async callback, it gets an error like so when attempting to invoke my mock service:

Unable to invoke endpoint URI "http://mycomputerlocation:8088/mockServiceCallbackBinding" successfully due to: javax.xml.soap.SOAPException: oracle.j2ee.ws.saaj.ContentTypeException: Not a valid SOAP Content-Type: text/html; charset=iso-8859-1

In the Error log, I get this:

Wed Sep 24 08:12:13 CDT 2014:ERROR:java.lang.NullPointerException
   java.lang.NullPointerException
    at java.io.StringReader.<init>(Unknown Source)
    at com.eviware.soapui.support.xml.XmlUtils.parseXml(XmlUtils.java:539)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockResponse.executeSpecifics(WsdlMockResponse.java:377)
    at com.eviware.soapui.impl.support.AbstractMockResponse.execute(AbstractMockResponse.java:268)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockOperation.dispatchRequest(WsdlMockOperation.java:227)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockDispatcher.dispatchPostRequest(WsdlMockDispatcher.java:256)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockDispatcher.dispatchRequest(WsdlMockDispatcher.java:122)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockRunner.dispatchRequest(WsdlMockRunner.java:156)
    at com.eviware.soapui.monitor.JettyMockEngine$ServerHandler.handle(JettyMockEngine.java:716)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Wed Sep 24 08:12:13 CDT 2014:ERROR:com.eviware.soapui.impl.wsdl.mock.DispatchException: java.lang.NullPointerException
   com.eviware.soapui.impl.wsdl.mock.DispatchException: java.lang.NullPointerException
    at com.eviware.soapui.impl.support.AbstractMockResponse.execute(AbstractMockResponse.java:284)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockOperation.dispatchRequest(WsdlMockOperation.java:227)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockDispatcher.dispatchPostRequest(WsdlMockDispatcher.java:256)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockDispatcher.dispatchRequest(WsdlMockDispatcher.java:122)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockRunner.dispatchRequest(WsdlMockRunner.java:156)
    at com.eviware.soapui.monitor.JettyMockEngine$ServerHandler.handle(JettyMockEngine.java:716)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
   Caused by: java.lang.NullPointerException
    at java.io.StringReader.<init>(Unknown Source)
    at com.eviware.soapui.support.xml.XmlUtils.parseXml(XmlUtils.java:539)
    at com.eviware.soapui.impl.wsdl.mock.WsdlMockResponse.executeSpecifics(WsdlMockResponse.java:377)
    at com.eviware.soapui.impl.support.AbstractMockResponse.execute(AbstractMockResponse.java:268)
    ... 17 more
Wed Sep 24 08:12:13 CDT 2014:ERROR:java.lang.IllegalStateException: WRITER
   java.lang.IllegalStateException: WRITER
    at org.mortbay.jetty.Response.getOutputStream(Response.java:594)
    at com.eviware.soapui.monitor.JettyMockEngine$MockRequestLog.log(JettyMockEngine.java:820)
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:51)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)