I am almost sure that this is not what the person asked you, but a standard 2D drawing exported from SU would look funny in AutoCad if one used the "hide" command. The export has no faces, so nothing happens there, but the section cut and profile edge lines are exported as wide polylines, and these lose their fill with Hide, and look meshy instead. Of course, a Regen brings all back to normal again.
Anssi