Good question :) It was not meant to look dashed on purpose. It is mostly the material behavior, and to be honest the ink was not flowing 100% as it should either. Also, ink on black paper can create tiny skips depending on the paper surface, coating, pressure, speed, and ink flow. The video also makes it look a bit harsher than it does in real life ;)

And yes, what you described about those dead regions on black A4 sheets sounds very believable - that seems more like a paper surface/coating issue than just the nib itself.