I do find the current item compare UI to be quite confusing, because it always shows the New/Equipped items in left to right order, and when the inventory is at the right side of the screen, that shows the equipped item closest to the thing you're mousing over, and the item you're hovering over on the far side.

It should ALWAYS show the item you're mousing over closest to the item, regardless of where the inventory screen is. It's just confusing otherwise.