Improper Format Duped Item

Bought a lantern prancer a while ago and recently noticed a trade on Outpost (http://www.tf2outpost.com/trade/5830026) with the same item for sale. The item has the same original ID as mine (546629264) and even lists me as the current owner in this trade. I believe that this item is duped but do not know enough about duped items to know how it was duped or who duped it. It seems likely that the poster of this trade (laskipukki) duped it as he still has it in his BP and shows up as a previous owner of the item in my BP. Any help with this issue would be greatly appreciated.

I did a little following up and it looks like this guy has duped multiple items. Here is a link to his valve profile.

http://steamcommunity.com/id/laskipukki/

Many high value items are duped. The people who originally duped them have been dealt with my Steam in varying ways. However Steam doesn't do anything else for duped items, the one you own will always be perfectly safe and never removed from the economy. If you feel you have been scammed (the trader tried to hide information from you pertaining to the trade) then you'll want to read this and fix this report to match the required format
http://forums.steamrep.com/threads/...-look-at-acceptable-format-before-posting.51/