Scrolling with the middle mouse button should lock the cursor in place relative to the screen. This would prevent edge-scrolling from triggering during the middle-mouse scroll (which is awful), and it will feel better to have middle mouse scrolling move only the view and not the cursor.

While a unit is selected, scrolling with middle mouse causes the game to re-compute pathfinding all the time, maybe because the cursor is moving. It makes middle mouse scrolling very jerky, especially at high framerates. This does not happen with edge scrolling or keyboard scrolling or without a unit selected, since paths are not being updated then.

Middle mouse button scrolling should both lock the cursor and disable pathfinding.