Sometimes when scrolling up, the view jumps. The behavior can be seen in any of the demos. Here's a screenshot video of it happening:
https://youtu.be/Sp7tjqWPc6I
Watch for when items 61 (and later, 96) come into view, and follow them with your eye. You'll see that they jump down quite a bit as scrolling continues. The mouse moves in circles to emphasize that the view has jumped.