So how and why did this happen to tradehill and not mtgox?
Surely the "scammer" would attempt to defraud the largest, already-proven-to-be-incompetent exchange, no?
It's possible Mt. Gox had the same thing happen and didn't notice. As I understand what they're saying, Dwolla just changed the status back to unpaid and took the money without any notification. If you weren't looking for something like that, you might not notice until some time later when you tried to balance the books.