onChange and DropDownList's - event not being dispatched

I can't get an onChange event to fire when making a ListItem selection in a DropDownList control. Am I doing something wrong? (I'm running XP Pro 32bit)

    
     var dlg = new Window('dialog');
     var pnl = dlg.add('panel');
     var myDDList1 = pnl.add('dropdownlist',undefined,['one', 'two', 'three'], {name: 'ddList1'});
     myDDList1.addEventListener('change', myFunction);
     var myDDList2 = pnl.add('dropdownlist',undefined,['one', 'two', 'three'], {name:'ddList2'});
     myDDList2.addEventListener('change', myFunction);
     var myDDList3 = pnl.add('dropdownlist',undefined,['one', 'two', 'three'], {name:'ddList3'});
     myDDList3.addEventListener('change', myFunction);
      function myFunction(ev)
     {
          var ddl = ev.target;
          var props = ddl.properties;
          if(props.hasOwnProperty('name'))
          {
               switch(props.name)
               {
                    case 'ddList1':
                        alert ('change made in ddList1');
                    break;
                    case 'ddList2':
                        alert ('change made in ddList2');
                    break;
                    case 'ddList3':
                        alert ('change made in ddList3');
                    break;
               }
          }
      
          ddl = null;
          props = null;
     };     
     dlg.show();