detectMultiScale returns incorrect face values

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Hi,

I am trying to detect faces from one image usinf face_cascade.detectMultiScale, but it returns a faces vector with 258235440 size. I'm using opencv 3.1.0 x86 version. Exploring the vector I can see that some values have x and y coordinates with negative values. The image actually does not conatins faces. The image is 1920x1080 24 bits rgb. The xml used is haarcascade_frontalface_alt.xml contained in data folder in opencv3.1.0 code.

This is my code:

    bool Util_Faces::detectFace(const cv::Mat &img, cv::Rect &rect)
{
    try
    {

        std::vector<cv::Rect> faces;
        float ratio = 5.0;
        float invertRatio = 1 / ratio;


        int newCols = (int)(img.cols*invertRatio);
        int newRows = (int)(img.rows*invertRatio);

        //Scale image to 1/5 factor. (Image is 1920x1080 24rgb
        cv::Mat imgGray;
        cv::resize(img, imgGray, cv::Size(newCols, newRows));

        cv::cvtColor(imgGray, imgGray, cv::COLOR_BGR2GRAY);

        //-- Detect faces
        Util_Faces::face_cascade.detectMultiScale(imgGray, faces, 1.1, 2, 0 | cv::CASCADE_SCALE_IMAGE);

        if (faces.size() == 0)
            return false;

        cv::Rect ajustRect = faces[0];
        rect = cv::Rect(ajustRect.x*ratio, ajustRect.y*ratio, ajustRect.width*ratio, ajustRect.height*ratio);

        return true;
    }
    catch (std::exception  ex)
    {
        int a = 0;
        return false;
    }


}

Anyone knows why am I receiving this values?

Thanks.