Replacing an item in the ObservableList of a ComboBox always changes the current selected item if the replaced position is before the selected positlion.


import javafx.application.*;
import javafx.collections.*;
import javafx.event.*;
import javafx.geometry.*;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.*;

public class ComboBoxModelTest2 extends Application {
    int i;

    ObservableList<String> model;

    public void start(Stage stage) {
        ComboBox<String> comboBox = new ComboBox<>();
        model = FXCollections.observableArrayList("Start 0", "Start 1", "Start 2");
        comboBox.itemsProperty().set(model);
        comboBox.getSelectionModel().select(1);

        Button button1 = new Button("Add");
        button1.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent arg0) {
                model.add("Item-" + (++i));
            }
        });
        Button button2 = new Button("Change First");
        button2.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent arg0) {
                model.set(0, "Change");
            }
        });

        VBox vbox = new VBox(7);
        vbox.setAlignment(Pos.CENTER);
        vbox.getChildren().addAll(comboBox, button1, button2);
        Scene scene = new Scene(vbox, 400, 400);
        stage.setScene(scene);
        stage.show();
    }
    
    public static void main(String[] args) {
        launch(args);
    }
}

Appending Items with the first button works as expected.
Replacing the first item in the list with the second button will shift the selection
toward the end.