Hi Phiro, that has to do with what are called "fully multiple knots" (corner points) in NURBS circles. If the control points around a fully multiple knot are modified so that the surface is not smooth there anymore it will get an edge added and the internal control point structure will have changed.

If you want a torus that squishes better with control point editing, use the Revolve command on it rather than sweeping it around a circle. (see attached file).

That will generate a true surface of revolution instead of a fitted spline surface like sweeping will create.

When MOI sees that you are turning on edit points on a surface of revolution it automatically rebuilds it so it does not have any internal corner points and should not generate any sharp edges after control point editing.

- Michael