Operating system: Windows XP SP2
JDK version: I found the bug in 1.4, 1.5, 1.6, 1.7

JSpinner increase/decrease buttons can have icons of different sizes. See the attached screen shot.

There is a test case:
============ Source Begin ===============
import javax.swing.*;
import java.awt.*;

public class JSpinnerArrowBug {
    private JFrame frame;

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                (new JSpinnerArrowBug()).setupUI();
            }
        });
    }

    private void setupUI() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JSpinner sp = new JSpinner(new SpinnerNumberModel(10, 1, 20, 1));
        sp.setPreferredSize(new Dimension(50, 25));
        frame.getContentPane().add(sp);

        frame.getContentPane().setLayout(new FlowLayout());
        frame.setSize(new Dimension(100, 100));
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}
============ Source End ================

Testing strategy:
1. Run the test
2. Note that the arrow icons have different sizes

Expected results:
Arrow icons have the same size

Actual results:
Arrow icon of the upper button is larger than the icon of the lower button.