I've noticed when selling gear via Trade, the things we sell disappear from the world and we get money. When we barter however, the items we sell appear in the merchants inventory (making it pretty easy to steal them back). Both have their positives and negatives. When I sell some uncommon/rare item I like the idea that I can buy it back one day if I have need of it. Conversely, it is so easy right now to rob merchants that it takes away from the joy and satisfaction of finding/earning gear through actual game play.
I don't know which behavior Larian intended, but the lack of consistency makes it feel like a bug. I would like consistency between the Trade/Barter menus. Maybe a happy middle-ground would be to only delete/destroy common, non-magical items?