pencil line with texture = errors

I am trying to use a pencil line with texture which looks nice but it produce lots of errors when rendered. They occur where the line overlaps itself, a hard edged white gap appears. It seems to be the same for any texture on the pencil line.

Has anyone got a solution for this?

I see it has been up before, but not resolved:
https://forums.toonboom.com/toon-boom-harmony/general-discussion/stange-gapsoverlaps-with-textured-pencil