usage of %IntBroker_Fault is not working in custom method.

We have implemented a web service where I am returning my custom message using %IntBroker_Fault. But the response used is not the soap fault instead it is using soap response message.

Scenario is: when I a validate a request parameter I am using %IntBroker_Fault to return my custom fault message, but the response is not bundled in Fault String instead the response is bundled in soap-body.

Sample Pseudo code is:
&var1 = &msg.rootnode.getParameter("abc");
If None(&var1) then
return customerrormthd();
end-if;

method customerrormthd()
&resmsg = createmessage(Operation.msg,%Intbroker_Fault)
&resmsg.setxmldoc("Customstring");
return &resmsg;
end-method;

With the above code My response is like below: