registerObjectMarshaller in Grails 1.1, suspected Bug

/* Book domain class */
class Book {
	int pages
	String title
}
 
/* Author domain class */
class Author {
	String name
	Date birthDate
}
 
/* registering custom marshallers in Bootstrap.groovy */
import grails.converters.JSON
 
class BootStrap {
 
	def init = { servletContext ->
		JSON.registerObjectMarshaller(Author){	author, json ->
			def birthday = author.birthDate
			json.build{
				"class(author)"
				id(author.id)
				name(author.name)
				info{
					birthdate(year: birthday.year, month: birthday.month, day: birthday.day)
				}
			}
		}
 
		JSON.registerObjectMarshaller(Book){	book, json ->
			json.build{
				"class(book)"
				id(book.id)
				info{
					pages(book.pages)
				}
			}
		}
	}
}
 
/* code for output in controller */
def list = {
	params.max = Math.min( params.max ? params.max.toInteger() : 10,  100)
	def authors = Author.list( params )
	withFormat{
		json{
			render authors as JSON
		}
		html{
			[ authorInstanceList: authors, authorInstanceTotal: Author.count() ]
		}
	}
}