I'm using POV v3.6.1c.icl8.win32, WinXP SP2.
I created a scene and put a simple sphere-sweep object in it.
There is a strange artifact only appearing on its shadow, not the object itself.

This is a simplified scene which is enough to show the problem:

#include "colors.inc"

camera {
  location  <-1.5, 0.3, -2.2>
  look_at   <-0.4, 0.3, -1>
}

light_source {
  <0,0.3,-3>
  color rgb White

polygon {
  4,
  <0, 0>, <0, 1>, <1, 1>, <1, 0>
  pigment { White }
  translate x*-0.5+y*-0.3
  scale 1.8
}

sphere_sweep {
  linear_spline
  2,
  < 0, -3, 3>, 1
  < 4, -5, 0>, 1
  pigment {Yellow}
  scale 1/20
  rotate x*-50
  translate -1.5*z+y*0.3
}

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In addition to my previous post:
The problem persists even when I change the sphere-sweep parameters to avoid
scaling. I have noticed an earlier post about "Scale dependant artifacts in
sphere_sweep", but changing the object's size to the values it would become
after scaling and removing the scale parameter won't help:

sphere_sweep {
  linear_spline
  2,
  < 0, -0.15, 0.15>, 0.05
  < 0.2, -0.25, 0>, 0.05
  pigment {Yellow}
  rotate x*-50
  translate -1.5*z+y*0.3
}

// the shadow still has artifacts

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It seems that in my case proportionally changing all of the sizes of the whole
scene to let the sphere_sweep be doubled in size solved the problem. The
sphere_sweep radius became 0.1, the shadow appearing correctly.

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