Changing XAxis title from chart.addChartDrillupListener does nothing

[mvysny]

Vaadin 8.8.6, Charts 4.2.0. The following code prints "Drillup" in the console when you drill up the charts (which means that the listener is called), but the X Axis title is not changed:

        chart.addChartDrillupListener(new ChartDrillupListener() {
            @Override
            public void onDrillup(ChartDrillupEvent event) {
                System.out.println("Drillup");
                x.setTitle("Changing title on drillup");
            }
        });

Steps to reproduce:

1. Click a bar in charts to drill down
2. Press the "Back to Browser brands" button.
3. The X Axis title should have been changed to "Changing title on drillup"

Workaround is to force chart redraw in the listener, by calling chart.drawChart(), however that interrupts the drillup animation.