Hi! I have kind of similar issue. I have completed all three parts of a quest, but sword didn't change at all (It says that I still have to solve the first riddle) thus, I can't drop it. Here is the link to a savegame: https://drive.google.com/file/d/0B6uSDZemTC4NemRNWkhMNDVCdEE/view?usp=sharing
P.S. I don't know if it helps, but I dug in in the save file (in MobileObjects.save) and found that this estoc still uses PX1_Curses_Weapon.prefab (I think that after finishing quest, this prefab should be removed and some enhancement prefabs added, right?)