There appear to be two different versions of some or all items on the steam market. For example, the Formal Body Shell: I can find one page for it here, and a different one here. The latter is the only one that shows up when I search for it, but if I just browse through the listings I see both. This applies to a lot of items, but is easier to see with higher rarities.
EDIT: the bug appears to be that each item is listed under its full name and its code name. Look at the urls given above.
go to the steam market, sort by price, browse backwards, look for dupes