Possible bug in cv::findCirclesGrid [closed]

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Hello

I am currently trying to calibrate my camera with the asymetric pattern of size(4,10). I created my own pattern similar to the standard pattern. The pattern is detected but the points are not ordered as you can see in the attached img

http://www.directupload.net/file/d/3771/odbq64he_png.htm

here is the original image:

http://www.directupload.net/file/d/3771/x35t6iep_png.htm

I use the standard detector with an adapted blob detector:

    SimpleBlobDetector::Params params;
    params.maxArea = 1e4;
    Ptr<FeatureDetector> blobDetector = new SimpleBlobDetector(params);

    grid_visible = cv::findCirclesGrid(img, m_markersize, positions, cv::CALIB_CB_ASYMMETRIC_GRID, blobDetector);

Is this just a bug or is there a some constraint on how the pattern has look like?