I am using the GetPointOnALine method in the MapSuiteCore v2.0.50727, here is the code snippet:
PointShape
pointShape = new PointShape();Vertex vertex0 = new Vertex(-76.61126, 39.293682);Vertex vertex1 = new Vertex(-76.61133, 39.294473);LineShape testLineShape = new LineShape();StartingPoint.FirstPoint, 50);
The resulting point shape has these coordinates - (X: -76.61126, Y: 39.294079045652289)
This looks like a rounding or some other kind of error with the longitude to me since the point really should be somewhere between -76.61126 and -76.61133. I'm using this function for one-way arrow placement so this seems to be what is throwing the placement off slightly in certain cases.
testLineShape.Vertices.Add(vertex0);
testLineShape.Vertices.Add(vertex1);
pointShape = testLineShape.GetPointOnALine(