Mat::push_back corrupts data (Bug #4421)

#include "opencv2/opencv.hpp" 

bool all_ones(const cv::Mat& m) {
  for (int i = 0; i < m.rows; ++i) {
    for (int j = 0; j < m.cols; ++j) {
      if (m.at<int>(i, j) != 1) {
        return false;
      }
    }
  }
  return true;
}

int main(int argc, char** argv) {
  cv::Mat data = cv::Mat::zeros(0, 128, cv::DataType<int>::type);

  for (int i = 0; i < 4; ++i) {
    printf("Iteration %d\n", i);
    cv::Mat to_append = cv::Mat::ones(3750000, 128, cv::DataType<int>::type);
    data.push_back(to_append);
    if (!all_ones(data)) {
      fprintf(stderr, "Error: not all elements are == 1.\n");
      exit(-1);
    }
  }

  return 0;
}

All elements of data should be equal to 1, but some elements become not equal to 1 after a few push_backs.

Output:

Iteration 0
Iteration 1
Iteration 2
Iteration 3
Error: not all elements are == 1.