Perhaps it's normal for the team who wrote the equation driven curves that the spline of the attached curve (which is NOT a spline, btw, so have not to be built after a Spline->Equation driven curve of the sketch menu, but would have its place in the Insert->Curves menu !!!!) so, the "spline" has to be fixed, with such construction, and it would be IMPOSSIBLE to drag it in the whole sketch, if equation driven curves would be well defined and well built !!!!!!
It's a bit frightful, yet, that a CAD program can stay which such bug at such basic level of the features, at the 20th release.