[Bug 2082009] [NEW] Tabbing through fields in a Java application periodically hangs text cursor

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The issue is that when I tab through the text fields in a Java
application, the text cursor periodically hangs. When this happens, the
cursor changes from a blinking line to a non-blinking line, and the
keyboard focus does not advance.

If I then press the "shift" key, then the window updates and the focus
advances to the next text field properly and the cursor starts blinking
again.

This issue started when we installed a new copy of Ubuntu 24.04.1 LTS,
We previously ran Ubuntu 22.04.5 LTS and the issue did not occur there.
The problem is occuring on multiple desktop systems.

While this issue occurred while running Java, I do not think that is a bug with Java (perhaps X11?)
I have tested with Oracle Java 17 and OpenJDK Java 21, and the problem occurs with both Java versions when running on Ubuntu 24.04.1 LTS, but not when running on Ubuntu 22.04.5 LTS.

We are using KDE as our window manager, but have also tried the Cinnamon
window manager and the problem still occurs when running Cinnamon.


Sample Java code to reproduce the issue:

import javax.swing.*;
import java.awt.*;

//
// This class is a simple program to demonstrate the issue. To run it:
// 1. Compile the program: javac TabBug.java
// 2. Run the program: java TabBug
//
public class TabBug extends JFrame {
    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(TabBug::new);
    }

    public TabBug() {
        super("Test Tabbing");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container pane = getContentPane();
        pane.setLayout(new GridLayout(9, 9));
        for (int i = 0; i < 81; i++) {
            pane.add(new JTextField(String.valueOf(i), 3));
        }
        setSize(600, 600);
        setVisible(true);
    }
}

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: openjdk-21-jre-headless 21.0.4+7-1ubuntu2~24.04
ProcVersionSignature: Ubuntu 6.8.0-44.44-generic 6.8.12
Uname: Linux 6.8.0-44-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.1-0ubuntu3.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Wed Sep 25 13:23:02 2024
ExecutablePath: /usr/lib/jvm/java-21-openjdk-amd64/bin/java
InstallationDate: Installed on 2024-09-06 (19 days ago)
InstallationMedia: Kubuntu 24.04.1 LTS "Noble Numbat" - Release amd64 (20240827)
SourcePackage: openjdk-21
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: openjdk-21 (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug noble
-- 
Tabbing through fields in a Java application periodically hangs text cursor
https://bugs.launchpad.net/bugs/2082009
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