Turning on "TitlePane.unifiedBackground" causes JInternalFrame menu bars to become translucent

[grimlock81]

I've been testing the new Unified backgrounds on Windows 10 feature. When I enable it as suggested with

UIManager.put( "TitlePane.unifiedBackground", true );

I find that the whole menu bar of any JInternalFrame become translucent and I can see beneath them to whatever is lying underneath. I've tried a few themes and they all have had it so I don't think it's related to any particular theme.

See this video

Test code below

import com.formdev.flatlaf.intellijthemes.FlatArcIJTheme;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;


public class TestTitlePaneUnifiedBackground {
    public static void main(String[] args) throws Exception {
        // comment this out and the bug no longer happens
        UIManager.put("TitlePane.unifiedBackground", true);
        EventQueue.invokeLater(() -> {
            try {
                startGUI();
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        });
    }

    private static void startGUI() throws Exception {
        try {
            UIManager.setLookAndFeel(new FlatArcIJTheme());
//            UIManager.setLookAndFeel(new FlatMonocaiIJTheme());
        }
        catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        }

        JFrame frame = new JFrame("Test Title Pane Unified Background");
        JDesktopPane desktopPane = new JDesktopPane();
        frame.add(desktopPane, BorderLayout.CENTER);

        JInternalFrame treeFrame1 = createInternalFrame("Test Tree 1");
        treeFrame1.setJMenuBar(createMenuBar("Tree", "Copy", "Paste", "Options"));
        desktopPane.add(treeFrame1);
        desktopPane.getDesktopManager().activateFrame(treeFrame1);
        JInternalFrame treeFrame2 = createInternalFrame("Test Tree 2");
        treeFrame2.setJMenuBar(createMenuBar("Menu", "Something", "Other", "Settings", "Blah"));
        desktopPane.add(treeFrame2);
        desktopPane.getDesktopManager().activateFrame(treeFrame2);

        frame.setJMenuBar(createMenuBar("File", "Edit", "View", "Help"));

        frame.setPreferredSize(new Dimension(800, 600));
        frame.pack();
//        frame.setExtendedState(Frame.MAXIMIZED_BOTH);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private static JInternalFrame createInternalFrame(String title) throws Exception {
        JInternalFrame internalFrame = new JInternalFrame(title, true, true, true, true);
        internalFrame.add(new JScrollPane(new JTree()));
        internalFrame.setBounds(0, 0, 800, 600);
        internalFrame.setMaximum(true);
        internalFrame.setSelected(true);
        internalFrame.setVisible(true);
        return internalFrame;
    }

    private static JMenuBar createMenuBar(String... menuNames) {
        JMenuBar menuBar = new JMenuBar();
        for (String name : menuNames) {
            menuBar.add(new JMenu(name));
        }

        return menuBar;
    }
}

[DevCharly]

Thx. Fixed in main branch.