ADDITIONAL SYSTEM INFORMATION :
Windows 7, also Redhat 8.2
Both OpenJDK 11.0.9 and OpenJDK 14.0.1

A DESCRIPTION OF THE PROBLEM :
In Java 8 it was possible to display an item in the ComboBox "button cell" which wasn't one of the items in the list
This functionality is mentioned in comments in javafx.scene.control.skin.ComboBoxListViewSkin.updateValue() suggesting it should be possible

// RT-21336 Show the ComboBox value even though it doesn't
// exist in the ComboBox items list (part one of fix)

Now in Java 11 (and 14) the behaviour has changed, the ComboBox displays blank

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the following. Press the button


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
"CHERRY" shown in ComboBox
ACTUAL -
ComboBox is blank

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class ComboBoxIssue extends Application {

    public enum Fruit {
        APPLE, BANANA, CHERRY
    }

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        ComboBox<Fruit> fruits = new ComboBox<>();
        fruits.getItems().addAll(Fruit.APPLE, Fruit.BANANA);
        fruits.setValue(Fruit.APPLE);
        Button button = new Button("Change");
        button.setOnAction(event -> {
            fruits.setValue(Fruit.CHERRY);
        });
        primaryStage.setScene(new Scene(new VBox(fruits, button)));
        primaryStage.show();
    }

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None known

FREQUENCY : always