While fishing in Abyssal, one would periodically catch a no drop item called Kutin's Key. A player could turn in infinite number of keys to Kutin and receive for each key, a potion of Essence of Troll (troll illusion) and a small amount of experience. The player could then turn around and sell this potion to an in game vendor for 50-57p depending on thier charisma.
The patch altered this. Now when one turns in the key, one still receives the teeny amount of experience but one receives instead a Potion of Transformation (troll illusion) instead. This potion is lore and no drop. So what they nerfed was the plat profit from selling the original potions back in game.