Platform: Windows XP SP2
JDK: 1.7

When JScrollPane has null border, the bottom and left scroll bar arrow icons are painted incorrectly. They are shifted by 1px. Please, find a screen shot in the attachment.

There is a test case:

=============== Source Begin ==============
import javax.swing.*;
import java.awt.*;

public class ScrollPanes extends JPanel {
    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                JFrame frame = new JFrame("JScrollPane arrow test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.getContentPane().add(new ScrollPanes());
                frame.setSize(512, 384);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public ScrollPanes() {
        super(new GridLayout(2, 2, 1, 1));

        JScrollPane leftScrollPane = new JScrollPane(createContent("ScrollPane has default border"));
        JScrollPane bottomScrollPane = new JScrollPane(createContent("ScrollPane border is null"));
        bottomScrollPane.setBorder(null);
        JScrollPane rightScrollPane = new JScrollPane(createContent("ScrollPane border is null"));
        rightScrollPane.setBorder(null);

        add(leftScrollPane);
        add(rightScrollPane);
        add(bottomScrollPane);
    }

    private JLabel createContent(String text) {
        JLabel label = new JLabel(text);
        label.setPreferredSize(new Dimension(500, 500));
        label.setHorizontalAlignment(JLabel.LEFT);
        label.setVerticalAlignment(JLabel.TOP);
        label.setOpaque(true);
        label.setBackground(Color.WHITE);
        return label;
    }
}
=============== Source End ==============


Testing strategy:
1. Run the test
2. Note that some scroll bar arrow icons are shifted by 1px (a screen shot in the attachment)

Current behavior:
Some scroll bar arrow icons are asymmetrical about the scroll bar center. They are shifted by 1 pixel.

Expected behavior:
All the scroll bar arrow icons are symmetrical about the scroll bar center.