Hang on, I'm not sure that I understand this correctly.  You credited an account with a certain amount of $ based on a report from one of your payment processors.  You then cleared the $ for a purchase order of BTC on your exchange, and this order was filled.  You then reversed this transaction because you realised that the payment processor hadn't actually cleared the funds.

My problem with this is that it's your responsibility to ensure that funds you allow onto the exchange are cleared, not the end user's.  If you let the funds on to the exchange then you're responsible for them.  You should not have reversed the transactions.  You should have covered the $ yourselves if the deposit turned out to be fraudulent.  I would see this responsibility as one of the core features of an exchange, otherwise it's just a glorified bulletin board. 

Am I wrong here?