Ah, bet he forgot to remove +1 destrier after the deal to Bugrahan. There is a bug that your trades won't clear after you've traded the actual item.
Here is an example:
I trade +1 Katana and 400k for an +2 Sword of War, but i also have an sale offer for lets say 400k.
Well the trade gets done, but the 400k money request for +1 Katana won't get deleted and this leads to scenario above, someone buys your new item(+2 SoW in this case) with the old items marketplace offer, which was sadly 400k.