It does not even have to be reported.
I have nothing against you or Coinbase and I do sincerely hope I am wrong. This can have dire consequences on your current and future business(es).
It would have been best to refund the withdrawal in its entirety or just credited it, to be used for a future transaction as that would have saved you guys from a world of pain.
For any other service I would have given you Kudos for acting, albeit slowly, and applauded honesty(though not so much due to blaming it on the servers, which in a financial context is unacceptable).
But for a business that a court can deem/classify as a financial institution (regardless if you consider yourself one), this could be considered as a admittance of wrong doing.
edit: grammar