When a list is so long that it rolls off the page with tasks and a user attempts to drag another task into that list at the bottom, scrolling down screws up Phabricator. The card no longer appears under the cursor, and can't be accurately placed in the destination list. This is compounded further by Phabricator's priority-based ordering of list items, so putting a card in the wrong "place" on a list can inadvertently change its global priority level.