Bezier curves are not circular arcs and Gcode can only describe a circular arc. Anything else is output as a series of straight lines.
In the past if you ran Gcode like this and got smooth motion then you would have been running in constant velocity mode. This would have had the controller trying to work out where you were going and then making up a toolpath that would allow it to get there without slowing down. The result is an approximation of what you wanted to cut. Masso runs exact stop so you get exactly what you ask for.
Cheers
Peter