FNCCalendar - AfterDrawDayNumbers constantly called when hovering with the mouse cursor


I wanted to use the Event "OnAfterDrawDayNumbers" to modify the appearance of the calendar.
Drawing things in the rectangle provided by the event seems to work fine. But while playing around with it i found a huge issue which basically leads the event being unusable for me.

Whenever the mousecursor hovers over the calendar, the event is being called constantly/the dates are getting repainted.

Is this behaviour intended? It seems like a huge flaw for performance reasons. I only discovered it because i was playing around with random colored ellipses that I added.
Or is there another way to add something to the background of the calendar dates?

I attached a demo project to show the behaviour.
FNCCalendarDemo.zip (9.6 KB)

This is by design, because it's a drawing event. When hovering over the calendar, the repaint instruction is called only when switching between dates. This triggers the OnAfterDrawDayNumbers. If you stick to drawing only, I can't see a reason why performance should be affected?