Spring MVC: CharacterEncodingFilter; why only set response encoding by force?

I was having a look at the CharacterEncodingFilter provided by Spring MVC. I was wondering why it was only possible to set the response encoding when the request encoding was forced to the given encoding? Why not be able to set a default response encoding if nothing is specified in the accept header fields? Or if no encoding was present in the request?

The code:

@Override
protected void doFilterInternal(
  HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
  throws ServletException, IOException {

  if (this.encoding != null && (this.forceEncoding 
      || request.getCharacterEncoding() == null)) {

    request.setCharacterEncoding(this.encoding);
    if (this.forceEncoding) {
      response.setCharacterEncoding(this.encoding);
    }
  }
  filterChain.doFilter(request, response);
}

I found this as reference https://jira.springsource.org/browse/SPR-3328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel stating that the response encoding can only be set when the request encoding is forcibly set. Why?

Thanks in advance, Martin