ADDITIONAL SYSTEM INFORMATION :
Reproduced in following combinations
 * RHEL 8.2 + OpenJDK 1.8.0_242 and OpenJDK 11.0.9
 * RHEL 8.6 + OpenJDK 17.0.5

Fault occurs on both physical hardware and VMWare Workstation Pro with 'cycle monitors' feature.



A DESCRIPTION OF THE PROBLEM :
Transparent windows implemented with Swing loose their transparency when either opened on secondary monitors or when they are dragged from primary to secondary monitor.

Investigation with xwininfo -all shows that when the window is on the primary monitor it has a bit depth of 32. When it is opened/moved to secondary monitor it switches to 24 bit depth.

Transparent windows implemented with JavaFX can be displayed without any issues on exactly the same JDK + RHEL setup.



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the test case on a RHEL 8.2+ environment with multiple monitors
Adjust the setLocation() call so the window appears on the secondary monitor

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Transparent window with semi-transparent red circle
ACTUAL -
Window with black background and red circle

---------- BEGIN SOURCE ----------
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class OverlayTest {

    public static void main(String[] args) {
        JPanel panel = new Custom();
        panel.setOpaque(false);
        panel.setBackground(null);
        JFrame frame = new JFrame();
        frame.setUndecorated(true);
        frame.setBackground(new Color(0, 0, 0, 0));
        frame.setTitle("TestOverlay");
        frame.getContentPane().add(panel);
        frame.setSize(320, 240);
        frame.setResizable(false);
        frame.setMinimumSize(new Dimension(1, 1));
        frame.setLocation(0, 0);
        frame.setVisible(true);
    }

    private static class Custom extends JPanel {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.clearRect(0, 0, getWidth(), getHeight());
            g.setColor(new Color(255, 0, 0, 127));
            g.fillOval(0, 0, getWidth(), getHeight());
        }
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
No known workaround

FREQUENCY : always