Jquery callbacks fired status killed by disable

JavaScript

var hello=function(a) {
};

var cb=$.Callbacks().add(hello);

alert('I expect this to be false and it is:' + cb.fired());
cb.fire('world');
alert('I expect this to be true and it is:' + cb.fired());
cb.disable()
alert('I expect this to be remain true but it is:' + cb.fired());