Program: 71218
Project: 71218
Buggy source:
public PropertiesSidebar(RootProperty root){
  super();
  this.root=root;
  this.setBackground(new Background(new BackgroundFill(Color.GREY,CornerRadii.EMPTY,Insets.EMPTY)));
  this.setMaxWidth(500);
  TreeItem<Property> rootNode=new TreeItem<>(root);
  setMapListener(rootNode);
  for (  Property property : root.getChildren().values()) {
    addNode(rootNode,property);
  }
  rootNode.setExpanded(true);
  TreeTableColumn<Property,String> nameColumn=new TreeTableColumn<>("String_Node_Str");
  nameColumn.setCellFactory(p -> new EditingCell(root));
  nameColumn.setOnEditCommit((p) -> {
    TreeTablePosition<Property,?> editingCell=p.getTreeTableView().getEditingCell();
    editingCell.getTreeItem().getValue().nameProperty.set(p.getNewValue());
  }
);
  nameColumn.setCellValueFactory(param -> param.getValue().getValue().nameProperty);
  TreeTableColumn<Property,String> dataColumn=new TreeTableColumn<>("String_Node_Str");
  dataColumn.setCellFactory(p -> new EditingCell(root));
  dataColumn.setOnEditCommit((p) -> {
    TreeTablePosition<Property,?> editingCell=p.getTreeTableView().getEditingCell();
    if (p.getRowValue().getValue() instanceof ParentProperty)     return;
    ((StringProperty)editingCell.getTreeItem().getValue()).valueProperty.set(p.getNewValue());
  }
);
  dataColumn.setCellValueFactory(param -> {
    if (param.getValue().getValue() instanceof ParentProperty)     return new ReadOnlyStringWrapper("String_Node_Str");
 else     return ((StringProperty)param.getValue().getValue()).valueProperty;
  }
);
  final TreeTableView<Property> treeTableView=new TreeTableView<>(rootNode);
  treeTableView.getColumns().add(nameColumn);
  treeTableView.getColumns().add(dataColumn);
  treeTableView.setShowRoot(false);
  treeTableView.setEditable(true);
  treeTableView.prefWidthProperty().bind(this.widthProperty());
  treeTableView.prefHeightProperty().bind(this.heightProperty());
  this.widthProperty().addListener((observable,oldValue,newValue) -> {
    setPrefWidths(newValue.intValue(),nameColumn,dataColumn,.55);
  }
);
  final String cssUrl1=getClass().getResource("String_Node_Str").toExternalForm();
  Main.root.getScene().getStylesheets().add(cssUrl1);
  this.getChildren().add(treeTableView);
}

Fixed version (ground truth):
public PropertiesSidebar(RootProperty root){
  super();
  this.root=root;
  this.setBackground(new Background(new BackgroundFill(Color.GREY,CornerRadii.EMPTY,Insets.EMPTY)));
  this.setMaxWidth(500);
  TreeItem<Property> rootNode=new TreeItem<>(root);
  setMapListener(rootNode);
  for (  Property property : root.getChildren().values()) {
    addNode(rootNode,property);
  }
  rootNode.setExpanded(true);
  TreeTableColumn<Property,String> nameColumn=new TreeTableColumn<>("String_Node_Str");
  nameColumn.setCellFactory(p -> new PropertyCell(root));
  nameColumn.setCellValueFactory(param -> param.getValue().getValue().nameProperty);
  TreeTableColumn<Property,String> dataColumn=new TreeTableColumn<>("String_Node_Str");
  dataColumn.setCellFactory(param -> new PropertyCell(root));
  dataColumn.setCellValueFactory(param -> {
    if (param.getValue().getValue() instanceof ParentProperty)     return new ReadOnlyStringWrapper("String_Node_Str");
 else     return ((StringProperty)param.getValue().getValue()).valueProperty;
  }
);
  final TreeTableView<Property> treeTableView=new TreeTableView<>(rootNode);
  treeTableView.getColumns().add(nameColumn);
  treeTableView.getColumns().add(dataColumn);
  treeTableView.setShowRoot(false);
  treeTableView.setEditable(true);
  treeTableView.prefWidthProperty().bind(this.widthProperty());
  treeTableView.prefHeightProperty().bind(this.heightProperty());
  this.widthProperty().addListener((observable,oldValue,newValue) -> {
    setPrefWidths(newValue.intValue(),nameColumn,dataColumn,.55);
  }
);
  treeTableView.setContextMenu(new PropertiesRootRClickMenu(root));
  final String cssUrl1=getClass().getResource("String_Node_Str").toExternalForm();
  Main.root.getScene().getStylesheets().add(cssUrl1);
  this.getChildren().add(treeTableView);
}