EndBulge when started may dramatically change the shape of degree 3 curves with 4 or 5 control points . This is a major problem, particularly when only a small adjustment to one end of the curve was intended. With 6 or more control points the curve remains unchanged until the user moves a control point. (A work around for curves with less than 6 control points is to first use InsertEditPoint to add control points without changing the shape of the curve. Then use EndBulge.)
EndBulge when used with degree 3 surfaces does not change the shape of the surface until the user moves a control point, even for single span surfaces. It should behave the same for curves.