The following source file causes an AssertionError in the internal compiler:

    public class Test
    {
        static class Outer
        {
            Outer(Inner inner) { }

            interface Inner { void f(); }
        }

        static class Foo extends Outer
        {
            Foo() { super(new Inner() { public void f() { Foo.this.notify(); } }); }
        }
    }

See http://statistics.netbeans.org/analytics/exception.do?id=202209 for the stacktrace.
Happens reproducably in NB 6.7 Beta.
Regression from NB 6.5, which doesn't cause an AssertionError with this example.