Interface and getClass() usage

Question

This is a repost of a thread I had in Java Programming Forum. It was not being answered so I though I would repost it here since their is some concept I must be missing.
Original is here http://forum.java.sun.com/thread.jsp?forum=31&thread=261941
If you answer this you will get the points there as well if you post there(so I can grant them).
public class A implements myInterface{}
public class B {
  public static void main(String [] vars){
    A a = new A();
    B b = new B();
    b.test(a);
  void test(myInterface interf){
    //Class c = interf.getClass(); //this throws NoSuchMethodError or NPE depending on -classic
    Class c = ((Object)interf).getClass(); //this always works
    System.out.println("class is " + c);
public interface myInterface {}Any ideas on this one? This is the actual code used to produce the error. JDK 1.3 and 1.4 too.

Answer 1

In fact it was not clearly explained. It was clearly explained why it should work, and I knew that it should before I even posted it. But it does not.
In the end I have concluded that it is JBuilders fault.
Before you point the finger let me assure you that the JRE is
java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Classic VM (build 1.3.1-b24, native threads, nojit)
I tried from the command line and this works fine. I tried in JBuilder and it does not. I not going to try and figure out why, thats Borland's job, but clearly they have a problem.