First time this had happened to me.
In one of the trader item lists today the top item kept flashing back and forth between to different items. I sold the trader some of my products and the item line jumped to the top. I went to sell some more and it started flashing (back and forth between skins and leather coats) back and forth. I am not sure if the the second item was at the top one the one I sold jumped to the top, but it continued flashing back and forth until the trader left.