Run attached code:

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.control.SelectionMode;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage stage) {
        ListView LV = new ListView();
        LV.setPrefHeight(100);
        LV.setPrefWidth(50);
        LV.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
        
        for (int i = 0; i < 20; i++) {
            LV.getItems().add(i, i);
        }
        
        Group root = new Group();
        
        root.getChildren().addAll(LV);
        stage.setScene(new Scene(root, 300, 300));
        stage.show();
    }
    
    public static void main(String[] args) {
        launch(Main.class, args);
    }
}

1) Select the first item
2) press shift+pageDown 2 times.
3) preff shift+pageUp 1 time.
See, selection is the first item only, but I expect 4-5 items to be selected.