OnException - out body length limited by input body length

[Martin Lichtin]

Using an <onException> to handle an exception, I  want to mark the situation as 
'handled' and set the body with information from the exception. Eg:

    <onException>
      <exception>java.lang.Exception</exception>
      <handled>
        <constant>false</constant>
      </handled>
      <setHeader headerName="Exchange.HTTP_RESPONSE_CODE">
        <constant>500</constant>
      </setHeader>
      <setBody>
        <simple>${exception.stacktrace}</simple>
      </setBody>
    </onException>
    
Problem is: the body is only filled up to the existing length of the input body.

For example, if the input body (e.g. of a POST request) is 10 characters, then 
the output body is also only 10 characters, filled with a little bit of the 
stack trace :)
Looks like a bug to me (using 2.18.4), or am I missing a way to properly set 
the output.

Thanks
- Martin