Zbrush | Problem ending curve line on the intersection of 2 polygroups and how to avoid them

On the neck with 2 Polygroups.

Let me start at the intersection of these two polygroups and see what happens.

I always try to pull it towards the angle I want the ring to appear.

It works as long as I have dragged past the borders or edge of the polygroups.

Then I can lightly tap on it to conform it to the contours of the neck.