BSplineCurve contructor ambiguous

[billpriest]

From BSplinCurve.h
BSplineCurve(std::vector &x, std::vector &y, int preferredDegree=3, double smoothing=0.0);
BSplineCurve(std::vector &knotX, std::vector &coefs, int degree);
I'm trying to construct an instance for the 2nd constructor
but because the signatures are identical with the 1st constructor given the default parameters the compiler complains as follows:

note: candidate: ‘fitpackpp::BSplineCurve::BSplineCurve(std::vector&, std::vector&, int)’
BSplineCurve(std::vector &knotX, std::vector &coefs, int degree);
^~~~~~~~~~~~
fitpackpp/fitpackpp/BSplineCurve.h:42:2: note: candidate: ‘fitpackpp::BSplineCurve::BSplineCurve(std::vector&, std::vector&, int, double)’
BSplineCurve(std::vector &x, std::vector &y, int preferredDegree=3, double smoothing=0.0);

Of course removing the default parameters allows it to compile and link. Maybe I'm missing something; but I don't think so.