Scale modify curve: mesh strays from the path

Hello guys.
I think I need some assistance with the scale modify curve. I drew a modifier curve on XY plane, but the farther I move the end vertex of the curve in both directions of the X axis, the more the mesh strays from the path curve. I don't recall experiencing this problem in the past.
Any ideas why this is happening?

Hi rubberDuck,

The scale modifier works in conjunction with the splines (the spline you are sliding) pivot location.

Select the spline you are going to slide, and use object [visual tools]"Pivot" (or "Object shortcut tools >> Pivot") to move its pivot point to bounded box center. It should then give the results expected.

Perfect! Thank you Steve!