Was the duplicating glitch i the game on purpose? I ask this because you cant duplicate all items.

i dont think it was, but who knows.

Sometimes items don't duplicate the first time you try, I tried duplicating azuras star like 50 times and it wouldn't work, on another day I tried it as I saw I had 3 scrolls that were the same and it worked, I still have 2 and gave one to Martin.