Item duped in normal trade

I was trading a low level item (16 Chaos for a ring). Player put stack of 10, then stack of 6 chaos, I put the ring in the trade window. We both accepted, and I ended up with 16 Chaos and the ring in my inventory...assuming the person also got the ring on their end (they never messaged me back).

Just happened at 21:14 GMT with this ring name: Armageddon Grasp, Ruby Ring

My concern is that this is either an item dupe bug (not sure how, I've traded thousands of times without any issues), or a bug where someone loses out on an item they were trading (in this case, the other person loses what they put in the trade window, and doesn't get the item they agree to).