Based on: https://forums.oracle.com/thread/2572732

iconifiedProperty does not work as expected when the application is maximized.

Can be reproduced using the following code and flow:

primaryStage.iconifiedProperty().addListener(new ChangeListener<Boolean>() {
            @Override
            public void changed(ObservableValue<? extends Boolean> observable, Boolean oldValue, Boolean newValue) {
                if (newValue) {
                    System.out.println("Locked");
                }
                else {
                    System.out.println("unLocked");
                }
            }
        });

Flow:
* Start application
* Maximize the application
* Minimize the application to lock it (iconifiedProperty is set to true).
* Click on the application to show it (iconifiedProperty is not triggered).
* Click maximize again to restore the application to its previous size and unlock (iconifiedProperty is set to false).