This one really caused me to scratch my head (and throw about 9 hours of production patterning away).
Draw a sphere.
Increase the isocurve display density to 9. This is fine and on a symmetrical object like a sphere it creates evenly spaced isocurves as you would expect.
Now move the surface seam to a new spot.
The surface isocurves are now randomly spaced. And of course the randomness is just a little too subtle to be seen by eye, so silly old me assumed everything was still evenly spaced.