I've noticed this issue a few times now. I go to buy something, and realize I don't have enough money during the purchase. I get prompted to buy currency, which I duly do. I then re-start the purchase. My money is taken (and by one vendor, taken twice) but I do not receive any goods (nor do I receive a refund).
It only seems to happen when I make purchase of currency during an existing purchase transaction, and has happened in a few places so is not limited to one vendor.
Can this be fixed?