Memory Leak in Mat::copyTo()

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I have a vector of images (called images) in OpenCV 3.0.0, which I iterate through in the way shown below. Please disregard, that this code makes no actual sense, I stripped it to point out the problem. Strangely, with each run the memory usage increases, even after the loop has completed. The way I see it, memory should stay the same, since the images in the images-vector are replaced. Manually releasing the matrices does not work either. What can I do to achieve constant memory usage.

for (int i = 0; i < num_images; ++i)
{
    Mat cropped_image;
    images[i].copyTo(cropped_image);
    images[i] = cropped_image;
}