If you have a JSplitPane containing a JScrollPane containing a JTree,
the scrollbar of the scrollpane disappears when you press the down
button on the divider, followed by the up button.

See test case below: (with JDK1.2FCS L)
1. Select 3 on the tabbed pane --> JTree is shown with scrollbar
2. Click down button on divider --> scrollbar disappears (OK)
3. Click up button on divider --> scrollbar should reappear

If you manually adjust the divider then the scrollbar reappears,
so the problem only appears to be with the one touch expandable
actions.

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.TreeUI;
import javax.swing.tree.*;
import javax.accessibility.*;



public class scrolltree extends JPanel {

        // Instantiate JtabbedPane, JScrollPane and JTree
        JTabbedPane tabbedPane = new JTabbedPane();
        JScrollPane msgScrollPane;
        JTree msgListPane;
        JButton red = new JButton("RED");
        JButton blue = new JButton("BLUE");
        Color clr;

    public scrolltree() {

                // Create default Tree and add to scollpane
                msgListPane = new JTree();
                JScrollPane msgScrollPane = new JScrollPane(msgListPane);
                msgScrollPane.setBackground(Color.green);

                tabbedPane.setBackground(Color.yellow);

                // Add panels to tabbedpane
                Component panel1 = makeTextPanel("One");
                tabbedPane.addTab("1", panel1);
                tabbedPane.setSelectedIndex(0);

                Component panel2 = makeTextPanel("Two");
                tabbedPane.addTab("2", panel2);

                Component panel3 = msgScrollPane;
                tabbedPane.addTab("3", panel3);

                JPanel p = new JPanel(new GridLayout(1,0));
                // Add listeners for buttons
                red.addActionListener(new RedListener());
                blue.addActionListener(new BlueListener());

                p.add(red);
                p.add(blue);

                JSplitPane jsp = new JSplitPane();
                jsp.setOneTouchExpandable( true );
                jsp.setOrientation( JSplitPane.VERTICAL_SPLIT );
                jsp.setLeftComponent( tabbedPane );
                jsp.setRightComponent( p );
                setLayout(new GridLayout(1,0));
                add( jsp );
    }
    protected Component makeTextPanel(String text) {
        JPanel panel = new JPanel(false);
        JLabel filler = new JLabel(text);
        filler.setHorizontalAlignment(JLabel.CENTER);
        panel.setLayout(new GridLayout(1, 1));
        panel.add(filler);
        return panel;
    }

    public static void main(String[] args) {

        JFrame frame = new JFrame("Color Tester");

        WindowListener l = new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        };
        frame.addWindowListener(l);

        frame.getContentPane().add(new scrolltree(), BorderLayout.CENTER);

        frame.setSize(400,180);
        frame.show();
    }

    class RedListener implements ActionListener
    {
        public void actionPerformed(ActionEvent evt)
        {
                msgListPane.setBackground(Color.red);
                clr = msgListPane.getBackground();
                System.out.println("Background color = " + clr);
        }
    }

    class BlueListener implements ActionListener
    {
        public void actionPerformed(ActionEvent evt)
        {
                msgListPane.setBackground(Color.blue);
                clr = msgListPane.getBackground();
                System.out.println("Background color = " + clr);
        }
    }
}