I was just in FM jumping up and down dropping items to a friend to scroll for me... and behold, my 99 attk stonetooth turned into 2........ O_O
Items can't be duplicated that easily, the most likely cause is that you had an extra one or looted one. If you are able to replicate it please PM a staff member.
I know i wasn't making it up b/c my inventory was full, and when I tried picking back up the 99 attk ST I coudnt cause my inventory was full and I still had one in the same spot in my inventory when I dropped it, but I will try to duplicate this and PM you if it occurs again.