Powerbi dev Question regarding visual refresh through Update() method in Typescript code

Hi,

I am building a custom Timeline visual. I expected the Update() method to refresh/repaint the visual cleanly without displaying the old bars/data. But I can still see the old visual/bars even when I want to completely overwrite and repaint it for new set of data.

I am referring to the Barchart visual where I see the data/bars being refreshed cleanly when the Update() is called each time you change the category name/measure data. 

what do you think I am missing here?

Appreciate any help on this!

Thanks

Sirisha