There is no GetPointAt() method. There are GetPointAtDist() and GetPointAtParam(). These are both the base Curve object methods, therefor the the GetPointAtDist() uses an absolute distance since it has no knowledge of a Station. On the other hand, the GetInstantaneousRadius() method is an Alignmnetobject method which DOES expect the actual Station value.
So no, it's not a bug, but it something to be aware of and have code that compensates for it.