Question about weird trade experience

Let me just write down what happened first.
I joined the buyer's game, we started the trade, put our stuff in the trade window (him 3 runes, me a

Hellfire Torch), pressed accept, and I thought we were done. I was in the process of thanking him in chat, when I saw him requesting to trade again. I accepted his request, and that's when I saw that I still had the torch I supposed to have traded with him in my inventory, but no runes. We repeated the trade process and ended up with the same results. He asked me if I had enough inventory space for the trade, which I did (I always leave 2 columns free to pick up stuff), so we tried again, and once again, the trade was unsuccessful. Then he created another game which I joined with a different character (with the exact same amount of free inventory space), tried to trade again, and this time it finally worked.
Could anyone tell me what went wrong in the first game? And, more importantly, if there is a way to prevent this from happening again.
I'm not the most tech savvy person, so it's entirelly possible that I muffed something up, and I'd really like to know what, because I was really worried that the buyer might think that I'm trying to scam him.

he was carrying a

Hellfire Torch.

or it was in his personal stash

Two reasons. One is correctly noted above, in order to receive a

Hellfire Torch via trade, you have to not carry one in your inventory AND not have one in your personal stash. I.e. your buyer needs to move his torch to his shared stash before a trade can complete. He may have remembered that and done that quickly at the start of the 2nd game.

Now, there is another reason however because there really is an "anti-trade" bug right now. I've had it happen twice (so it is fairly rare, considering how many trades/trade games I've done) for no apparent reason. I know both sides had enough room (same item size guarantees that, if you don't know your opposite to confirm) and it wasn't any limited items like torch or

Gheed's. Soon as the 2nd person hit accept, the trade window just closed and nothing happened, no matter how often you tried.
First time we just both ended up dropping our stuff on the Ground to trade. Second time around, we made a new game and that seemed to fix it.

Oh, bugger, I should have thought to ask the buyer if he had a torch in his inventory or his personal stash, but this simple solution just didn't cross my mind until I saw your answers. Silly me.
Or maybe he didn't have a torch yet, and we just had the misfortune to encounter this "anti-trade" bug you speak of, Schnorki.
Either way, thank you for the answers, and for putting my mind at ease, fellas!

I've encounetred the trade bug three times even though my trade count is less than 100. Two times (as Schnorki said) I've just dropped items on the Ground, once the accepted trade became successful on 5 or 6 try.