Steps to reproduce:
- Run the following code with option -Dsun.java2d.uiScale=1.5
- Drag the internal frame
There are line artifacts on the desktop pane
-------------------------
import javax.swing.*;
import java.awt.BorderLayout;

public class DragInternalFrameTest {

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(DragInternalFrameTest::UI);
    }

    private static void UI() {

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        JDesktopPane desktopPane = new JDesktopPane();

        frame.add(desktopPane, BorderLayout.CENTER);
        frame.setSize(700, 500);
        frame.setLocation(100, 100);
        frame.setVisible(true);

        JInternalFrame internalFrame = new JInternalFrame("Test");
        internalFrame.setSize(200, 200);
        desktopPane.add(internalFrame);
        internalFrame.setVisible(true);

        frame.setLocation(0, 0);
        frame.setVisible(true);
    }
}
-------------------------