FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b104)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b104, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
pressing arrow-key-down in a jlist with both scrollbars visible,
first visible index > 0 and select index > visible index makes the list
jumping down


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
you can test this with the attached small program.
just be sure to adjust the window to have both scrollbars visible,
scroll down to have the visible index > 0 then scroll up some items
and down again


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
no jumping list
ACTUAL -
jumping list

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.DefaultListModel;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class JScrollBarTest {

  public static void main(String[] args) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel p = new JPanel(new BorderLayout());
    JList l = new JList();
    DefaultListModel dlm = new DefaultListModel();
    for (int i = 0; i < 100; i++)
      dlm
        .addElement(i
          + " asdjafljasdlfu earp9tuepr9g uepr9t7u " + "wiphdfkjvnasdasdlasdjalsdaksdhaksdhaskjdhaskdhakdhasfkhsadlfh");
    l.setModel(dlm);
    JScrollPane s = new JScrollPane(l);
    l.setSelectedIndex(99);
    l.ensureIndexIsVisible(99);
    p.add(s, BorderLayout.CENTER);
    f.getContentPane().add(p);
    f.pack();
    f.setSize(new Dimension(200, 400));
    f.setVisible(true);
  }

}

---------- END SOURCE ----------

Release Regression From : 6
The above release value was the last known release where this 
bug was not reproducible. Since then there has been a regression.