为什么函数getLayoutBounds（）。getHeight（）在文本组件上返回两个不同的值？

Question

示例代码：

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.scene.layout.Pane;
import javafx.scene.text.Font;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class TestSpecialLibrary extends Application {

    Text text;
    TextField text4;

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

        Pane root=new Pane();
        root.setPrefWidth(600);
        root.setPrefHeight(300);

        text=new Text("AqgWT");
        text.setLayoutX(0);
        text.setLayoutY(200);

        TextField text1=new TextField("AqgWT");
        text1.heightProperty().addListener(new ChangeListener<Number>() {
            @Override
            public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
                if (newValue!=oldValue){
                    setDimensionFont(text1);
                }  
            }
        });
        text1.setLayoutX(0);
        text1.setLayoutY(0);
        text1.setPrefWidth(200);
        text1.setMinHeight(1);
        text1.setMaxHeight(500);
        text1.setPrefHeight(25);

        TextField text3=new TextField();
        text3.setLayoutX(300);
        text3.setLayoutY(30);
        text3.setPrefWidth(50);
        text3.setMinHeight(1);
        text3.setMaxHeight(500);
        text3.setPrefHeight(25);

        text4=new TextField();
        text4.setLayoutX(300);
        text4.setLayoutY(0);
        text4.setPrefWidth(50);
        text4.setMinHeight(1);
        text4.setMaxHeight(500);
        text4.setPrefHeight(25);

        Button bs1=new Button("bs1");
        bs1.setLayoutX(220);
        bs1.setLayoutY(0);
        bs1.setPrefWidth(50);
        bs1.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                text1.setPrefHeight(10+text1.getPrefHeight());
            }
        });

        Button bs2=new Button("bs2");
        bs2.setLayoutX(380);
        bs2.setLayoutY(0);
        bs2.setPrefWidth(50);
        bs2.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                text1.setFont(new Font(text1.getFont().getName(),
                        20));
                text.setFont(new Font(text1.getFont().getName(),
                        20));
                text4.setText(String.valueOf(text.getLayoutBounds().getHeight()));
            }
        });

        root.getChildren().add(text1);
        root.getChildren().add(bs1);
        root.getChildren().add(text4);
        root.getChildren().add(bs2);
        root.getChildren().add(text);
        Scene scene = new Scene(root);

        stage.setScene(scene);
        stage.show();
    }

    private void setDimensionFont(TextField txt){
            Font font=txt.getFont();
                font=new Font(font.getName(),20);
                text.setFont(font); 
                double height = Math.round(text.getLayoutBounds().getHeight()) 
                    + txt.getPadding().getTop() + txt.getPadding().getBottom();
                double p3=Math.round(text.getLayoutBounds().getHeight());
                if (height<=txt.getHeight()){
                    txt.setFont(font);
                    txt.positionCaret(txt.getCaretPosition());
                    text4.setText(String.valueOf(p3));
                }

    }

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

}

当我点击按钮bs1时，我更改了prefHeight text1的TextField，因此函数setDimensionFont启动，字体大小更改为20，而text4中显示的值为text.getLayoutBounds().getHeight()是27岁。

然后我点击bs2，这个字体大小总是在20，但现在text.getLayoutBounds().getHeight()的值是30 ......为什么？