Offset produces a bad result for the simple single span degree 3 (Bezier) curve in the attached file. The result is a polycurve with discontinuous curvature (C1 continuity) between the two constituent curves. This occurs with offset curves on both sides of the input curve. The offset of a curve should have the same continuity as the input curve unless there is a kink due to the offset distance being too large. That is not the situation with this curve.
The offset distance varies from the specified 5 to 5.056 (Offset distance was measured as the distance from the input curve to the offset curve along a curve perpendicular to the input curve.) This is also an error.
Input curve in black. Offset curve in blue. OffsetBug2.3dm (1.7 MB)