[jQuery] Callback from the $.post function is not being invoked

[mistere357]

I'm new to jQuery and it has worked great for me...
   except I seem to be having a problem with the $.post function.
The response comes back but the callback function is not invoked.

Here is the loop that I'm using to set the onChange event handler:

datafields = new Array( "#field1", "#field2", "#field3" ) ;
function edit_event_handlers( ) {
   for ( var target in datafields ) {
       $(datafields[target]).change( function(dft) {
           return function() {
               $(dft).css('background-color','orange') ;
               var params = { fieldname: dft.replace("#",""),
fieldval: $(dft).val() }
               $.post("/index.php/Workflow_server/updatefield/",
                   params,
                   function(){ alert("Data returned") ; }, "xml"
               ) ;
           }  ;
       }(datafields[target]) ) ;
   } ;
}

Using firebug I see the params are sent to the server process and the
xml data is returned:
 (it just wraps $_POST in <test> tags)

<test>array(2) {
  ["fieldname"]=> string(7) "#field1"
  ["fieldval"]=> string(6) "345345"
}
</test>

... but the alert in the function never appears.
I also tried this line for the function parameter of the $.post call
without success:

   function() { return function(rdata){ alert("Data returned: " +
rdata)  } }

What am I missing here?

Thanks,
Eric