Hi Dave, that's just a display artifact, there isn't anything actually wrong with your object.

Curves are drawn very accurately by breaking them down to within one pixel of their true shape, so they are adaptive to the current zoom level.

It's too expensive to draw shaded surfaces in that type of dynamic way so they are drawn differently, by breaking them down to triangles in object space and then those triangles are drawn. You're just seeing an area there where the triangle structure is more obvious and just happens to deviate by just a hair from the accurate curve display.

These types of display artifacts should just be ignored, don't try to do anything to "fix" them, it's just a normal part of the display engine that it will not make a perfect looking display because it is focused a lot on doing things quick. If it tried to make a pixel perfect display that would unfortunately be much slower and you'd have to wait all the time after doing any modeling operation for the display to update.

Hope that helps explain it!

- Michael