Dragging an index card away from the infinite board edge causes the board to resize down a more compact size. Unfortunately this happens WHILE you are dragging the card, which causes some stuttering/jumping as the scrollbars resize and the screen recenters.
To resolve this, I would say don't allow board resizing while you're dragging a card.
Edit: To clarify, only prevent SHRINKING of the board while dragging a card. Expanding the board doesn't cause jerky dragging effects.