I found a bug with in dhtmlx 3.0 dealing with Calendar events. The events for onChange and onClick are reversed.
myCoreDetails.getCalendar( “taken_date” ).attachEvent(“onClick”,function(date, state){
alert("Date is changed to " + date)
});
myCoreDetails.getCalendar( “taken_date” ).attachEvent(“onChange”,function(date, state){
alert("Date is changed to " + date)
});