Ok, I think I have it figured out - the current mod doesn't recognize the fact that this item is already enhanced (with Dull Copper), and therefor isn't adding in the durability kick from the enhancement -
vs
(and yes, if I had the 10 crystal shards, I'd probably kick it up to 50DI - I'd of preferred for it to have been a straight dragon slayer, but oddly, Lava Serpent Crust is a lot easier to gather than White Pearls...)