Comment 3 for bug 1516244

>Where is the bug?

If the graphic line width on the edge.cuts layer work as you describe, then one has to calculate different coordinates for the board outline versus what the actual coordinates of the lines defining them are.
I don't see this kind of thinking applied anywhere else in KiCAD nor any other CAD package I've been working with in the last 15 years?
This means cutouts would need to be undersized for coordinate input, while board outline coordinate inputs would need to be oversized.. and all that depending on the chosen line width?