Strange... with the previous sharpen, the added agility requirement per level was 6,7,8,9,10 (didn't check higher). For the new sharpen, it is 6,7,8,9,10,12,13,14
Since you learned the new skill to level 5, this means additional damage of 47-64. Based on the agility remaining the same, this implies you sharpened it on level 5 previously, and not on any of the previous levels. However, the previous level 5 damage bonus was 16-33, so the damage should have gone up if this were the case.
It seems the damage bonus with the new sharpen skill replaces the previous bonus, but the agility requirement for the weapon may not be handled properly.