Bug in TF1::FixParameter (TGraph::Fit)

ROOT
1

Hello, try this code with ROOT 5.30/04:

    TF1 *f = new TF1("resolution_function_square", "1 . / (x / 1000.) ++ 1. / (x * x / 1000. / 1000.)     ++ 1", 0.01, 1000E5);
    f.FixParameter(1, 10);
    cout << "par1: " << f.GetParameter(1) << endl; // 10
    TGraph gr;
    gr.SetPoint(0, 1, 1);
    gr.SetPoint(1, 2, 2);
    gr.SetPoint(2, 3, 3);
    gr.Fit(f, "Q");
    cout << "par 0: " << f.GetParameter(0) << endl; // 10
    cout << "par 1: " << f.GetParameter(1) << endl; // != 10

what I’m doint is fixing the parameter 1 to be equal to 10 and fittining. After the fit parameter 1 is different to 1, but parameter 0 is equal to 10.