ByteArrayMessageElement and StringMessageElement

Hello folks,
 I don't know what's going wrong, but I am trying to send a String through a 
JxtaBiDiPipe and
I am getting strange results. By the way, I am running the producer and 
receiver on the same
machine, different threads.
 The producer part is like this:
 Message msg = new Message();
StringMessageElement el = StringMessageElement("MESSAGE", "Hello World!", 
null);
msg.add("MESSAGE", el);
client.send(msg);
 On the other hand, the receiver part is like this:
 StringMessageElement me = (StringMessageElement) msg.getElement("MESSAGE");
me.toString();
 The message gets delivered, but I noticed that I always receive a 
ByteArrayMessageElement,
in spite of sending a StringMessageElement !!! 
 Anyone here has a clue about this?
 Edward