Steps to reproduce:

1) Run test code below
2) Scroll horizontally to right-most position
3) Note that the column headers no longer align to the cell borders

import java.util.stream.Collectors;
import java.util.stream.IntStream;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.property.SimpleStringProperty;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class FXTableViewExample10 extends Application {
    public static void main(String [] args) {
        Application.launch(args);
    }
     
    @Override
    public void start(Stage primaryStage) {
        TableView<Integer> table = new TableView<>();
        table.setFixedCellSize(24);
         
        // rows
        table.getItems().addAll(IntStream.range(0, 100).boxed().collect(Collectors.toList()));
         
        // columns & cells
        for (int j=0; j<100; j++) {
            int colNr = j;
            TableColumn<Integer, String> col = new TableColumn<>(String.format("Col %02d", j));
            col.setCellValueFactory(feat -> new SimpleStringProperty(String.format("%02d.%02d", colNr, feat.getValue())));
            table.getColumns().add(col);
        }
         
        Scene scene = new Scene(table, 500, 475);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}