When inserting items in a ListView (or TableView), the scroll position is kept relative to the whole content. If the scroll position is at 50% and we double the number of items, the position is still at 50% thus showing a completely different section. I would expect that the current view section does not change, otherwise the list is not usable anymore while adding items concurrently.

Here's some demo code:

import java.util.Timer;
import java.util.TimerTask;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class ListScrollTest extends Application {
  @Override
  public void start(Stage primaryStage) throws Exception {
    Scene scene = new Scene(new VBox(), 400, 200);
    
    // a list containing 20 items
    ListView<String> listView = new ListView<>();
    for (int i = 0; i < 20; i++) {
      listView.getItems().add("item " + i);
    }
    listView.getSelectionModel().select(10);
    listView.scrollTo(10);
    
    // add new items at the bottom concurrently
    new Timer().schedule(new TimerTask() {
      @Override
      public void run() {
        Platform.runLater(new Runnable() {
          public void run() {
            listView.getItems().add("make list unusable");
          }
        });
      }
    }, 2000, 200);
    
    ((VBox) scene.getRoot()).getChildren().addAll(listView);
    
    primaryStage.setScene(scene);
    primaryStage.show();
  }
  
  public static void main(String[] args) {
    launch(args);
  }
}