by Ken Golliher:
Your bank "accepted" the cashiers check when your employee signed it. You cannot change your mind and stop payment. That's why cashiers checks are required at real estate closings and other financial events where people want to be certain they have good funds.
Your bank is not obligated to replace a customer's check with a cashiers check. Personal opinion strongly held: It's a truly ridiculous practice that indicates the issuing bank simply does not comprehend its own actions.
by John Burnett:
Setting aside the question of stopping payment on the cashier's check, which isn't possible, assuming the stop payment on your customer's check had been available to your teller at the time he or she cashed the check, you clearly have a retraining issue.