The compiler is currently rejecting this code:

public class X {
    abstract class Base {}
    interface Marker {}
    sealed class B extends Base {}
    final class C extends B implements Marker {}
    private <T extends Base & Marker> void test(T obj) {
        B b = (B) obj; //error - cannot convert T to B
    }
}

this seems like a bug in the current implementation of the sealed classes spec (reported offline by Jan)