Timeline.setVerticalGridLines doesn't do anything

I’m trying to set VerticalGridLines with the Vaadin timeline add-on.

I’m using following calls:

What I see is that the range is picked up by the timeline (it shows numbers on the VerticalAxis between 0 and 100000), so that’s ok, but whatever I try the timeline refuses to draw the GridLines at the specified intervals (10, 20, 30, etc.).

Any idea what I am doing wrong? Is there something else I need to do with the timeline in order to set the VerticalGridLines ?

Thanks,
Kim Marivoet