bug in cv::blur (Bug #3345)

Test:

TEST(Blur, Mat)
{
    Size kernelSize(3, 3);

    /// ksize > src_roi.size()
    Mat src(3, 3, CV_8UC1, cv::Scalar::all(255)), dst;
    Mat src_roi = src(Rect(1, 1, 1, 1));
    src_roi.setTo(cv::Scalar::all(0));

    blur(src_roi, dst, kernelSize, Point(-1, -1), BORDER_REPLICATE);
    std::cout << "ksize > src_roi.size() (works like BORDER_ISOLATED - why????? ):\n";
    std::cout << "src: " << std::endl << src << std::endl;
    std::cout << "src_roi: " << std::endl << src_roi << std::endl;
    std::cout << "dst: " << std::endl << dst << std::endl;

    /// ksize <= src_roi.size()
    src = Mat(5, 5, CV_8UC1, cv::Scalar(255));
    src_roi = src(Rect(1, 1, 3, 3));
    src_roi.setTo(0);
    src.at<uchar>(2, 2) = 255;

    blur(src_roi, dst, kernelSize, Point(-1, -1), BORDER_REPLICATE);
    std::cout << "\nksize <= src_roi.size() (works like !BORDER_ISOLATED - default behavior):\n";
    std::cout << "src: " << std::endl << src << std::endl;
    std::cout << "src_roi: " << std::endl << src_roi << std::endl;
    std::cout << "dst: " << std::endl << dst << std::endl;
}

Output:

ksize > src_roi.size() (works like BORDER_ISOLATED - why???? ):
src: 
[255, 255, 255;
  255, 0, 255;
  255, 255, 255]
src_roi: 
[0]
dst: 
[0]

ksize <= src_roi.size() (works like !BORDER_ISOLATED - default behavior):
src: 
[255, 255, 255, 255, 255;
  255, 0, 0, 0, 255;
  255, 0, 255, 0, 255;
  255, 0, 0, 0, 255;
  255, 255, 255, 255, 255]
src_roi: 
[0, 0, 0;
  0, 255, 0;
  0, 0, 0]
dst: 
[170, 113, 170;
  113, 28, 113;
  170, 113, 170]

but in the first case dst must be [227]