The system is automatic and upon receiving on funds they appear in the recipient's account.
However, as I said, we missed a payment method which appeared as instant to our system, but was marked as pending in the payment provider's system. This also triggered the manual check and led to the taken actions.
Maybe you should add payment methods progressively and take enough time to thoroughly test them instead of rolling trades back after the fact. Just saying.
I'll give you a little piece of advice, I don't mean to lecture to you or stuff but your official statement missed two things : "We apologize" and "it's fixed now". Here's how I would have communicated about that : "We made a little a mistake while implementing this payment gateway, we didn't properly check that the payment was final before crediting the user account. This is now fixed. We apologize to our users for the inconvenience and will do our best to not make the same mistake again. We didn't have a choice but to rollback the trades that came after this bug because ".
Your communication so far makes it look like you threw something together pretty fast in order to get your share of the bitcoin exchange market without taking enough time to thoroughly test the software. Being generally dismissive (towards users, and security flaws reporters) doesn't really help either.
My point basically boils down to : change the way you communicate and you will reap lots of benefits in term of positive user feedback and general perception.