ADDITIONAL SYSTEM INFORMATION :
Windows 11 24H2

A DESCRIPTION OF THE PROBLEM :
Java seems to paint the background of a component in two different ways depending on when the painting is done. It looks like a rounding issue when the display scaling is greater than 100%. The difference is a 1 pixel line on the right or at the bottom of the component that is not repainted. One consequence is trailing segments appearing when components are dragged across a container.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Set the display scaling to 125%.
Create a JPanel with black background in a JFrame at (x, y), with width and height 40.
Through a Timer (10 ms is enough), change the background to white and call the repaint() method of the panel.
Try with different values for (x,y): (0,0), (0,1), (0,2)...

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The panel should be a white square.
ACTUAL -
Depending on the values of (x,y), black 1 pixel width lines appear at the right and/or at the bottom of the square.
Note that there is a regular pattern in the way the lines appear as you increase the x and y values.

---------- BEGIN SOURCE ----------
package HDPI;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;


@SuppressWarnings("serial")
public class HdpiPaintIssue extends JFrame {

public class TestPanel extends JPanel {

@Override
protected void paintComponent(Graphics g) {

super.paintComponent(g);

updateInfo((Graphics2D) g);
}

private void updateInfo(Graphics2D g2d) {

Integer X = getX();
Integer Y = getY();
labelX.setText("x = " + X.toString());
labelY.setText("y = " + Y.toString());

final AffineTransform t = g2d.getTransform();
final Double tx = t.getTranslateX();
final Double ty = t.getTranslateY();

labelTX.setText("tx = " + tx.toString());
labelTY.setText("ty = " + ty.toString());
}
}

private final Color light = Color.white;
private final Color dark = Color.black;

private TestPanel panel = null;
private JLabel labelX = null;
private JLabel labelY = null;
private JLabel labelTX = null;
private JLabel labelTY = null;

public HdpiPaintIssue() {

super("HDPI issue");
setSize(250, 200);
setLocationRelativeTo(null);
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
setVisible(true);
setFocusable(true);
requestFocus();

getContentPane().setLayout(null);


// Labels to display a few values

labelX = new JLabel();
labelX.setBounds(100, 2, 40, 24);
getContentPane().add(labelX);

labelY = new JLabel();
labelY.setBounds(100, 14, 40, 24);
getContentPane().add(labelY);

labelTX = new JLabel();
labelTX.setBounds(150, 2, 100, 24);
getContentPane().add(labelTX);

labelTY = new JLabel();
labelTY.setBounds(150, 14, 100, 24);
getContentPane().add(labelTY);

JLabel lbVersion = new JLabel("java.version = " + System.getProperty("java.version"));
lbVersion.setBounds(50, 140, 120, 24);
getContentPane().add(lbVersion);


// Panel to be moved

panel = new TestPanel();
panel.setBounds(0, 0, 40, 40);
panel.setOpaque(true);
panel.setBackground(dark);
getContentPane().add(panel);

delayedRepaint();


// Buttons to move the panel

addButton("<", 80, 80);
addButton(">", 140, 80);
addButton("^", 110, 50);
addButton("v", 110, 110);
}

private void addButton(String text, int x, int y) {

JButton b = new JButton(text);
b.setBounds(x, y, 50, 30);
getContentPane().add(b);
b.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
            
             Point pt = panel.getLocation();
             switch(text) {
             case "<":
             pt.x = pt.x - 1;
             break;
             case ">":
             pt.x = pt.x + 1;
             break;
             case "^":
             pt.y = pt.y - 1;
             break;
             default:
             pt.y = pt.y + 1;
             }
     panel.setBackground(dark);
     panel.setLocation(pt); // <- setLocation() triggers a dark painting
     delayedRepaint(); // <- we trigger a light painting on top of it
            }
        });
}

private void delayedRepaint() {

Timer timer = new Timer(10, new ActionListener() { // A short delay is required for the issue to appear
@Override
public void actionPerformed(ActionEvent arg0) {
panel.setBackground(light);
             panel.repaint();
}
});
timer.setRepeats(false);
timer.start();
}

public static void main(String args[]) {

SwingUtilities.invokeLater(new Runnable() {
public void run() {
new HdpiPaintIssue();
}
});
}
}
---------- END SOURCE ----------