I do a bit of concept stuff don't think of myself as a concept artist but I am trying to help so here goes.
When i do this stuff I section off areas, i take it your trying to draw a continuous line or want to, i.e. without lifting the pen tablet?
I agree with mod it is a bit confusing to know what is going on exactly.
I am at most times at 1px even if the image is 8000 x 8000 or something, and i think that is a small resolution compared to other concept artists. Then again i am still learning how to do things myself.
Good luck perhaps come back if we haven't fixed the issue or if you fixed the issue yourself and perhaps drop that into the thread so anyone having that issue as well can get the solution you provided.
It is a thought, either way I am interested to know what the issue exactly was or how you fixed it.
Another thing that came to mind is if you want clean continuous lines I'd get Illustrator with the pen tool to create the line art you can draw the line stop then draw it again, fix the lines and even make them thicker so this could solve the issue as a whole.
Yes i type too much.