It seems that all the Adidas stores on the avatar marketplace were reset yesterday. I am not sure if any of the items are new, but a lot of items were officially relisted as new even though they were old items. Furthermore, ALL adidas items appear to have been "unofficially" delisted and relisted.
I own a large amount of Adidas items and the "already purchased" shopping cart flag has been removed from all of them. In other words, I am now able to waste my money and buy them again if I so wish.
I checked my other avatar items and they are the same as before, so the problem is exclusive to the Adidas stores.
I have not tested to see if I am able to re-download my previously purchased Adidas items using my Download History, as this seems like it would be a big risk and I may lose access to my old purchases by attempting this.