Program: 90840
Project: 90840
Buggy source:
public SettingsPanel(){
  root=new DefaultMutableTreeNode(new SettingsNodeData("String_Node_Str",null));
  model=new DefaultTreeModel(root);
  tree=new FullWidthSelectionJTree(model);
  breadcrumbs=new JPanel();
  breadcrumbs.setLayout(new BoxLayout(breadcrumbs,BoxLayout.LINE_AXIS));
  breadcrumbs.setBorder(new EmptyBorder(5,5,5,0));
  setBreadCrumbs(root);
  final CardLayout cardLayout=new CardLayout();
  pages=new JPanel(cardLayout);
  tree.setEditable(false);
  tree.setSelectionRow(0);
  tree.setRootVisible(false);
  tree.setShowsRootHandles(true);
  tree.setExpandsSelectedPaths(true);
  tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
  final DefaultTreeCellRenderer renderer=new DefaultTreeCellRenderer();
  renderer.setIcon(null);
  renderer.setLeafIcon(null);
  renderer.setOpenIcon(null);
  renderer.setClosedIcon(null);
  renderer.setBackgroundNonSelectionColor(getBackground());
  final Color bg=renderer.getBackgroundSelectionColor();
  tree.setBackgroundSelectionColor(bg);
  tree.setCellRenderer(renderer);
  tree.getSelectionModel().addTreeSelectionListener(new TreeSelectionListener(){
    @Override public void valueChanged(    final TreeSelectionEvent e){
      final DefaultMutableTreeNode selectedNode=(DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
      if (selectedNode != null) {
        setBreadCrumbs(selectedNode);
        final SettingsNodeData data=(SettingsNodeData)selectedNode.getUserObject();
        if (data.page != null)         cardLayout.show(pages,data.page.getTreePath());
      }
    }
  }
);
  final JButton cancel=new JButton("String_Node_Str");
  final JButton apply=new JButton("String_Node_Str");
  final JButton ok=new JButton("String_Node_Str");
  final JPanel buttons=new JPanel();
  buttons.setLayout(new BoxLayout(buttons,BoxLayout.LINE_AXIS));
  buttons.add(Box.createHorizontalGlue());
  buttons.add(cancel);
  buttons.add(apply);
  buttons.add(ok);
  final JPanel content=new JPanel(new BorderLayout());
  content.add(breadcrumbs,BorderLayout.NORTH);
  content.add(pages,BorderLayout.CENTER);
  content.setBorder(new EmptyBorder(10,0,10,10));
  final JScrollPane treeScrollPane=new JScrollPane(tree);
  treeScrollPane.setPreferredSize(new Dimension(500,500));
  treeScrollPane.setBorder(new MatteBorder(0,0,0,1,Color.LIGHT_GRAY));
  final JSplitPane splitPane=new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,treeScrollPane,content);
  splitPane.setResizeWeight(0);
  splitPane.setContinuousLayout(true);
  splitPane.setDividerSize(10);
  splitPane.setDividerLocation(300);
  splitPane.setBorder(new MatteBorder(0,0,1,0,Color.LIGHT_GRAY));
  this.setLayout(new BorderLayout());
  this.add(splitPane,BorderLayout.CENTER);
  buttons.setBorder(new EmptyBorder(10,0,5,10));
  this.add(buttons,BorderLayout.SOUTH);
  runOnCancel=new ArrayList<>();
  runOnOk=new ArrayList<>();
  cancel.addActionListener(e -> cancel());
  ok.addActionListener(e -> {
    getPages().forEach(SettingsPage::apply);
    runOnOk.forEach(Runnable::run);
  }
);
  apply.setEnabled(false);
  modificationListener=() -> apply.setEnabled(true);
  apply.addActionListener(e -> {
    apply.setEnabled(false);
    getPages().forEach(SettingsPage::apply);
  }
);
}

Fixed version (ground truth):
public SettingsPanel(){
  root=new DefaultMutableTreeNode(new SettingsNodeData("String_Node_Str",null));
  model=new DefaultTreeModel(root);
  tree=new FullWidthSelectionJTree(model);
  breadcrumbs=new JPanel();
  breadcrumbs.setLayout(new BoxLayout(breadcrumbs,BoxLayout.LINE_AXIS));
  breadcrumbs.setBorder(new EmptyBorder(5,5,5,0));
  setBreadCrumbs(root);
  final CardLayout cardLayout=new CardLayout();
  pages=new JPanel(cardLayout);
  tree.setEditable(false);
  tree.setSelectionRow(0);
  tree.setRootVisible(false);
  tree.setShowsRootHandles(true);
  tree.setExpandsSelectedPaths(true);
  tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
  final DefaultTreeCellRenderer renderer=new DefaultTreeCellRenderer();
  renderer.setIcon(null);
  renderer.setLeafIcon(null);
  renderer.setOpenIcon(null);
  renderer.setClosedIcon(null);
  renderer.setBackgroundNonSelectionColor(tree.getBackground());
  final Color bg=renderer.getBackgroundSelectionColor();
  tree.setBackgroundSelectionColor(bg);
  tree.setCellRenderer(renderer);
  tree.getSelectionModel().addTreeSelectionListener(new TreeSelectionListener(){
    @Override public void valueChanged(    final TreeSelectionEvent e){
      final DefaultMutableTreeNode selectedNode=(DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
      if (selectedNode != null) {
        setBreadCrumbs(selectedNode);
        final SettingsNodeData data=(SettingsNodeData)selectedNode.getUserObject();
        if (data.page != null)         cardLayout.show(pages,data.page.getTreePath());
      }
    }
  }
);
  final JButton cancel=new JButton("String_Node_Str");
  final JButton apply=new JButton("String_Node_Str");
  final JButton ok=new JButton("String_Node_Str");
  final JPanel buttons=new JPanel();
  buttons.setLayout(new BoxLayout(buttons,BoxLayout.LINE_AXIS));
  buttons.add(Box.createHorizontalGlue());
  buttons.add(cancel);
  buttons.add(apply);
  buttons.add(ok);
  final JPanel content=new JPanel(new BorderLayout());
  content.add(breadcrumbs,BorderLayout.NORTH);
  content.add(pages,BorderLayout.CENTER);
  content.setBorder(new EmptyBorder(10,0,10,10));
  final JScrollPane treeScrollPane=new JScrollPane(tree);
  treeScrollPane.setPreferredSize(new Dimension(500,500));
  treeScrollPane.setBorder(new MatteBorder(0,0,0,1,Color.LIGHT_GRAY));
  final JSplitPane splitPane=new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,treeScrollPane,content);
  splitPane.setResizeWeight(0);
  splitPane.setContinuousLayout(true);
  splitPane.setDividerSize(10);
  splitPane.setDividerLocation(300);
  splitPane.setBorder(new MatteBorder(0,0,1,0,Color.LIGHT_GRAY));
  this.setLayout(new BorderLayout());
  this.add(splitPane,BorderLayout.CENTER);
  buttons.setBorder(new EmptyBorder(10,0,5,10));
  this.add(buttons,BorderLayout.SOUTH);
  runOnCancel=new ArrayList<>();
  runOnOk=new ArrayList<>();
  cancel.addActionListener(e -> cancel());
  ok.addActionListener(e -> {
    getPages().forEach(SettingsPage::apply);
    runOnOk.forEach(Runnable::run);
  }
);
  apply.setEnabled(false);
  modificationListener=() -> apply.setEnabled(true);
  apply.addActionListener(e -> {
    apply.setEnabled(false);
    getPages().forEach(SettingsPage::apply);
  }
);
}