To reproduce: make any window focused and then make the app focused

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class RT30511 extends Application {

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

    @Override
    public void start(Stage stage) throws Exception {

        HBox root = new HBox(20d);

        TextField textField = new TextField("سمَـَّوُوُحخ ̷̴̐خ ̷̴̐خ ̷̴̐خ امارتيخ ̷̴̐خ");
        root.getChildren().add(textField);

        Scene scene = new Scene(root, 300, 250);

        stage.setScene(scene);
        stage.setTitle(System.getProperty("java.runtime.version") + "; " + System.getProperty("javafx.runtime.version"));
        stage.show();
    }
}