Grails 1.1.2 breaks update action on a domain class with a relationship to another domain class which has a constraints block.

Grails 1.1.2 breaks update action on a domain class with a relationship to another domain class which has a constraints block.

Consider the very simple classes below:

class Author {
String name
static constraints = {}
}

class Book {
Author author
}

class BookController {
def scaffold = true
}

class Bootstrap {
def init = { servletContext ->
new Author(name:'Fred').save()
new Author(name:'James').save()
}

The error is:

Error 500: java.lang.ClassCastException: Author$_clinit_closure1 cannot be cast to java.util.Map

Test case:

Create a new book with author 'Fred'.
On the 'Show Book'page, press the 'Edit' button
On the 'Edit Book' page, press the 'Update' button (don't change the author)

As mentioned, when a different author is chosen, the update works fine. When the Author class has no constraints, the update works fine too.
I have not seen this problem in 1.1.1.