Con il pannello crei il binding solo con i components: risolvi facendo a manina via script..

codice:
// supponendo che il WebServiceConnector si chiami "connector"
import mx.data.binding.EndPoint
import mx.data.binding.Binding

var srcEndPoint:EndPoint	= new EndPoint();
var endEndPoint:EndPoint	= new EndPoint();
srcEndPoint.component		= connector;
srcEndPoint.property		= "results";
srcEndPoint.event		= "result";
endEndPoint.component		= casella_txt;
endEndPoint.property		= "text";
var listToDesc:Binding = new Binding(srcEndPoint, endEndPoint);

connector.trigger();