This evening I received an incoming trade, adding two copies of Creeping Renaissance to my inventory. After marking the cards as received and going into my inventory, I had four copies (two with details, two without), but the inventory item was still flagged (with the two-way arrow icon) as having two inbound copies. The trade referenced when looking at the details behind the icon was the one I had just received.

UPDATE: The same seems to be true of all of my recent trades. The cards are flagged as involved in a trade, even if the cards have been received and marked as such.