Something wrong with my scratchboard tool

Okay I've been using Painter 12, and just today I've downloaded the Painter 2019 trial. When I use the scratchboard tool this happen:

See what the arrow is pointing at, for some reason when I do a stroke, sometimes that happened. It doesn't happen in painter 12 though.  So is that a bug or some sort of new feature. If so, how do I turn it off or adjust it.

Thank You