groovy.lang.MissingMethodException when calling method isAttached on domain class

Steps to reproduce:
1) Create a fresh grails 2.0.RC1 application

grails create-app grails2-test-app; cd grails2-test-app

2) Create a domain class:

grails create-domain-class grails2.test.domain.Book

3) Add a property to the domain class:

class Book {
  String title
  static constraints = { }
}

4) Create a controller:

grails create-controller grails2.test.controller.Book

5) Add the following code to the generated index action.

def index() { 
  def book = new grails2.test.domain.Book(title: 'yyyy')
  println book.isDirty()
  println book.isAttached()
  render 'If you do not see this message something went wrong!'
}

5) Run the application and navigate to this URL in your browser: http://localhost:8080/grails2-test-app/book/index

As you can see on your browser, the exception is thrown only in the call to method isAttached. Other domain class dynamic methods like isDirty does not throw exception. According to grails 2.0.0RC1 http://grails.org/doc/2.0.0.RC1/ref/Domain%20Classes/isAttached.html the method is supported in this version.