Program: 32307
Project: 32307
Buggy source:
@Override public void registerExtenderCallbacks(final IBurpExtenderCallbacks callbacks){
  this.callbacks=callbacks;
  callbacks.setExtensionName(NAME);
  stdout=new PrintWriter(callbacks.getStdout(),true);
  stderr=new PrintWriter(callbacks.getStderr(),true);
  helpers=callbacks.getHelpers();
  SwingUtilities.invokeLater(new Runnable(){
    @Override public void run(){
      panel=new JPanel();
      scroll=new JScrollPane(panel,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
      scroll.setBorder(BorderFactory.createEmptyBorder());
      JLabel shLabel=new JLabel("String_Node_Str");
      JLabel portLabel=new JLabel("String_Node_Str");
      JLabel interfaceLabel=new JLabel("String_Node_Str");
      portField=new JTextField(Integer.toString(port));
      interfaceField=new JTextField(ip);
      requestHookURLField=new JTextField(requestHookURL);
      JButton saveButton=new JButton("String_Node_Str");
      saveButton.addActionListener(new ActionListener(){
        @Override public void actionPerformed(        ActionEvent e){
          stdout.println("String_Node_Str");
          saveConfig();
        }
      }
);
      GroupLayout layout=new GroupLayout(panel);
      panel.setLayout(layout);
      layout.setAutoCreateGaps(true);
      layout.setAutoCreateContainerGaps(true);
      GroupLayout.SequentialGroup hGroup=layout.createSequentialGroup();
      hGroup.addGroup(layout.createParallelGroup().addComponent(interfaceLabel).addComponent(portLabel).addComponent(shLabel).addComponent(saveButton));
      hGroup.addGroup(layout.createParallelGroup().addComponent(interfaceField).addComponent(portField).addComponent(requestHookURLField));
      layout.setHorizontalGroup(hGroup);
      GroupLayout.SequentialGroup vGroup=layout.createSequentialGroup();
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(interfaceLabel).addComponent(interfaceField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(portLabel).addComponent(portField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(shLabel).addComponent(requestHookURLField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(saveButton));
      layout.setVerticalGroup(vGroup);
      restoreConfig();
      callbacks.customizeUiComponent(scroll);
      callbacks.addSuiteTab(BurpExtender.this);
    }
  }
);
}

Fixed version (ground truth):
@Override public void registerExtenderCallbacks(final IBurpExtenderCallbacks callbacks){
  this.callbacks=callbacks;
  callbacks.setExtensionName(NAME);
  stdout=new PrintWriter(callbacks.getStdout(),true);
  stderr=new PrintWriter(callbacks.getStderr(),true);
  helpers=callbacks.getHelpers();
  SwingUtilities.invokeLater(new Runnable(){
    @Override public void run(){
      panel=new JPanel();
      scroll=new JScrollPane(panel,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
      scroll.setBorder(BorderFactory.createEmptyBorder());
      JLabel shLabel=new JLabel("String_Node_Str");
      JLabel portLabel=new JLabel("String_Node_Str");
      JLabel interfaceLabel=new JLabel("String_Node_Str");
      portField=new JTextField(Integer.toString(DEFAULT_PORT));
      interfaceField=new JTextField(DEFAULT_IP);
      requestHookURLField=new JTextField(DEFAULT_REQUEST_HOOK_URL);
      JButton saveButton=new JButton("String_Node_Str");
      saveButton.addActionListener(new ActionListener(){
        @Override public void actionPerformed(        ActionEvent e){
          stdout.println("String_Node_Str");
          saveConfig();
        }
      }
);
      GroupLayout layout=new GroupLayout(panel);
      panel.setLayout(layout);
      layout.setAutoCreateGaps(true);
      layout.setAutoCreateContainerGaps(true);
      GroupLayout.SequentialGroup hGroup=layout.createSequentialGroup();
      hGroup.addGroup(layout.createParallelGroup().addComponent(interfaceLabel).addComponent(portLabel).addComponent(shLabel).addComponent(saveButton));
      hGroup.addGroup(layout.createParallelGroup().addComponent(interfaceField).addComponent(portField).addComponent(requestHookURLField));
      layout.setHorizontalGroup(hGroup);
      GroupLayout.SequentialGroup vGroup=layout.createSequentialGroup();
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(interfaceLabel).addComponent(interfaceField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(portLabel).addComponent(portField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(shLabel).addComponent(requestHookURLField));
      vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(saveButton));
      layout.setVerticalGroup(vGroup);
      restoreConfig();
      callbacks.customizeUiComponent(scroll);
      callbacks.addSuiteTab(BurpExtender.this);
    }
  }
);
}