OnEventBubble won't fire

This is in my view:

@Html.DayPilotBubble("bubble", new DayPilotBubbleConfig { CssOnly = true, CssClassPrefix = "bubble_default" })

@Html.DayPilotScheduler("dps", new DayPilotSchedulerConfig()
{
...
EventBubble = "bubble",
...
})

Serverside I got this in my DayPilotScheduler:

protected override void OnEventBubble(EventBubbleArgs e)
{
e.BubbleHtml = "Event details for id: " + e.Id;
}

When I hover an event nothing happens. I'm NOT assigning any value to BubbleHtml (or StaticBubbleHTML for that matter) in OnBeforeEventRender.

If I set a breakpoint inside OnEventBubble it won't get hit. There's no ajax call occuring either when I hover an event.
How do I make dynamic event bubble work?