more vertex points than necessary for curves

if you generate a curve like this:

vector<ofVec2f> control;
...
ofPath path;
path.curveTo(control.front());
for(int i = 0; i < control.size(); i++) {
  path.curveTo(control[i]);
}
path.curveTo(control.back());
ofPolyline polyline = path.getOutline()[0];
cout << polyline.size() << endl;

the number of points in the polyline are more than necessary. it looks like at each control point, vertices are doubled up -- except for the beginning, where there is only one vertex.

i discovered this while trying to smoothly interpolate along a polyline, and found that the vertices weren't evenly spaced.

Reproduce the example with ofPath::curveTo and inspect the ofPolyline returned by path.getOutline()[0], comparing vertex counts and spacing around control points. Trace the curve and outline-generation entry points used by these APIs; done means redundant vertices are removed and interpolation along the resulting polyline has even spacing.