Iconifying and restoring a stage by clicking on the taskbar icon works fine.
However, if the stage is maximized, iconifying only works once; after restoring the stage the iconifyProperty isn't update, also it's not updated when iconifying again. Only after un-maximizing the stage, the behavior returns to normal-

{code}
public class Main extends Application {

  @Override
  public void start(Stage primaryStage) throws Exception {
    VBox root = new VBox();

    Button iconifyButton = new Button("Iconify");
    iconifyButton.setOnAction(event -> primaryStage.setIconified(true));

    Button maximizeButton = new Button("Maximize");
    maximizeButton.setOnAction(event -> primaryStage.setMaximized(!primaryStage.isMaximized()));

    root.getChildren().addAll(iconifyButton, maximizeButton);

    primaryStage.iconifiedProperty().addListener((observable, oldValue, newValue) -> {
      System.out.println("Iconified: " + newValue);
    });
    primaryStage.maximizedProperty().addListener((observable, oldValue, newValue) -> {
      System.out.println("Maximized: " + newValue);
    });

    primaryStage.setTitle("Hello World");
    primaryStage.initStyle(StageStyle.UNDECORATED);
    primaryStage.setScene(new Scene(root, 100, 100));
    primaryStage.show();
  }


  public static void main(String[] args) {
    launch(args);
  }
}
{code}