Persistence of embedded items in subclasses

I have the following domain classes:

class SiteUser {
String login
String password
String nick
String status = "active"
Date signUpDate = new Date()
}

class Customer extends SiteUser {
String firstName
String lastName
String telephone
Address address

static constraints =

static embedded = ['address']
}

class Address {
String street
String zipcode
String country
}

When I execute the following on the console I get two strange things:

def newuser = new SiteUser(login:'base@site.com', password:'aasa132',nick:'tester')
if (newuser.save())
{
println 'Success'
def all = SiteUser.list()
print all
}
else {
newuser.errors?.allErrors.each

}

First, an exception is raised and the user is not saved, but even so, newuser.save() is returning TRUE.

Second, the exception is "Caused by: java.sql.SQLException: Column 'ADDRESS_COUNTRY' cannot accept a NULL value.", when Address is not a field of SiteUser but one of its subclasses.

Reviewing the database, both SiteUser and its subclasses are stored on the same table, but the address fields (ADDRESS_COUNTRY, ADDRESS_ZIPCODE, ADDRESS_STREET) are declared as NOT NULL.

Creation of SiteUser objects is failing because of one of its subclasses, even though the field on that subclass is nullable. It seems that this is because the fields on the Address class are not nullable, and they're being used for the declaration regardless of the fact that the address field is nullable itself.

PS: if I declare the following subclass:

class AdminUser extends SiteUser {
String adminValue

static constraints =

}

The table field adminValue is correctly declared as nullable, probably to avoid problems like the one above.