FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

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

A DESCRIPTION OF THE PROBLEM :
When a MouseListener is added to a JScrollbar, the events are not triggered when you click on any of the arrow buttons.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
-Create a Jframe with a JScrollPane and a component and make sure that at least the horizontal scroll bar shows up.
-Add a mouse listener adapter and implement the mouseclick method.
-Click on the toolbar's thumb control, you will see the event is triggered.
-Click on any of the arrow buttons, you will see nothing happens.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Events should be triggered when acting over the arrow buttons since they are part of the JScrollPane
ACTUAL -
Nothing happens when you click on the arrow buttons, that is, the event is not triggered.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class MouseScrollbar extends JFrame
{
    JTextArea _ta = new JTextArea();
    int i = 0;
    public MouseScrollbar()
    {
        super("Test Scrollbar");
        JScrollPane sp = new JScrollPane(_ta);
        getContentPane().add(sp,BorderLayout.CENTER);
        _ta.setPreferredSize(new Dimension(600,600));
        setDefaultCloseOperation(MouseScrollbar.DISPOSE_ON_CLOSE);
        setSize(400,400);
        
        // This listener is not triggered when you click on the arrow buttons.
        sp.getHorizontalScrollBar().addMouseListener(new MouseAdapter(){

            @Override
            public void mouseClicked(MouseEvent e)
            {
                _ta.setText(_ta.getText()+"\n"+"Mouse clicked (" + (++i) + ")");
            }});
    }
    
    public static void main(String params[])
    {
        MouseScrollbar msb = new MouseScrollbar();
        msb.setVisible(true);
        System.out.println(System.getProperty("java.version"));
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
You can get the two arrow buttons and add the events to each one. Something like this:

        Component comp[] = scrollbar.getComponents();
        for (int i=0;i<comp.length;i++)
        {
            if (comp[i] instanceof BasicArrowButton)
            {
                comp[i].addMouseListener(ma);
            }
        }

You could also try to override JScrollbar's addMouseListener