Why does masonry cards have magic padding?

Question

css

Bootstrap 4, if you put 2 columns in Cards-columns https://v4-alpha.getbootstrap.com/components/card/... Then the padding will be incomprehensible, the next element from the bottom will be pushed down. And there will be an empty space

In the example in the photo:

.card-columns {
                    -webkit-column-count: 2;
                    -moz-column-count: 2;
                    column-count: 2;
                }

And so when viewing the code:

If you set 1, 3, 4+ columns, everything is ok, there is no padding at the bottom.
How to fix?