The XMLStreamWriter.close method says:

  /**
   * Close this writer and free any resources associated with the 
   * writer.  This must not close the underlying output stream.
   * @throws XMLStreamException 
   */
  public void close() 
    throws XMLStreamException;

but Zephyr implements it as:

    /**
     * Close the underlying stream to which data is being written.
     * @throws XMLStreamException if an error occurs while closing the stream.
     */
    public void close() throws XMLStreamException {
        fReuse = true;
        try{
            fWriter.close();
        }catch(IOException ioexception){
            throw new XMLStreamException(ioexception);
        }
    }

... which is against the spec.