can get mouse events with javac but not gcj ... what's wrong?

Java code NoMouse.java is at the bottom of this posting.
NoMouse works with javac but not gcj.
You test by moving moving mouse in-and-out-of-window:
   $ javac NoMouse.java ; java NoMouse
   mouseEntered
   mouseEntered
   mouseEntered
   ...
But I do _not_ get "mouseEntered" whin compiling with gcj:
   $ gcj --main=NoMouse NoMouse.java ; ./a.out
What am I doing wrong? Is there a workaround?
How can I get mouse events when using gcj?

--- NoMouse.java follows ---

import java.awt.event.*;
import javax.swing.*;
public class NoMouse extends JFrame {
    public static void main(String [] args) { new NoMouse(); }
    public NoMouse() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(500, 300);
        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent e) {
                System.out.format("mouseEntered\n");
            }
        });
        setVisible(true);
    }
}