Observe the following image of a pipe created by beveling a Bezier curve using a Bezier circle.
Note the apparent defect in the object; it appears inside the red colored circle I have drawn upon the image. If the object is converted into a mesh or a N.U.R.B.S. curve then the defect no longer appears. What causes it and what, if anything apart from the aforementioned solutions, can be done to eliminate it?