Should be. Unfortunately, the Supreme Court ruled that an officer doesn't have to know the law to enforce it, implying that you as a citizen will get in trouble if an officer tells you to do something as long as he thinks he's enforcing a law.

These days, the only thing you can do with any reliability is exercise your right to a lawyer. Even then, you had better hope the officer isn't having a bad day, because there's no repercussion for him for just arresting you then and there.