JQuery validate plugin: error not unsetting in dependent field

[seezee]

Using the jQuery Validate plugin, I've got a group of 3 radio buttons, 'foo[]'; if the user selects #foo0, then #fooDetail is not required, but if the user selects either #foo1 or #foo2, #fooDetail is required:

var $req = "required"; 
foo: $req,
fooDetail: { 
     required: function(element) { 
          return $("#foo1").is(":checked")||$("#foo2").is(":checked"); 
     } 
},

The problem is, if someone selects #foo1 or #foo2, changing the selection back to #foo0 doesn't unset the error message on #fooDetail. I've also tried

          return $("#foo0").not(":checked");

which doesn't work either. Does anyone know how to deal with this?