getDeclaringClass throws error

[rrva]

Hi

Why does the following testcase fail with IncompatibleClassChangeError ?

package foo;

import javassist.*;

import org.junit.*;

public class GetDeclaringClassTest {

    static class Foo {
        String bar;
    }

    @Test
    public void get_declaring_class_should_not_throw_error()
            throws NotFoundException, CannotCompileException {
        ClassPool pool = ClassPool.getDefault();
        CtClass cc = pool.get(Foo.class.getName());
        cc.setName(Foo.class.getName() + "$BackRef");
        Class<?> klass = cc.toClass();
        klass.getDeclaringClass();

    }
}

[rrva]

Error was

java.lang.IncompatibleClassChangeError: foo.GetDeclaringClassTest and foo.GetDeclaringClassTest$Foo$BackRef disagree on InnerClasses attribute

Is it because I have not modified the outer class? How can I create a copy of a inner class (and add one field) without getting this error?