Nothing hurts quite like looking at your online bank statement the day the mortgage is transferred out. Nothing, except seeing that money transferred out twice. Ouch. Some Citibank customers using the company’s new payment app were seeing double payments, because of an error in processing. The New York Times reports:

The problem, which began in July but went undetected by the bank until December, prompted bogus payments big and small. Some customers quickly spotted the redundant transaction and complained to Citi, while other consumers were caught off guard when the bank recently notified them of the discrepancy. The snag even led some unsuspecting customers to overdraw their accounts, though a bank spokesman said that was rare.

Also rare: kids on school buses, popcorn at the movies, and water in swimming pools.

Citi says the problem was limited to its iPad app - if you tried to make a payment using your iPad, and the transaction failed, Citi’s system was set to automatically re-try the transaction. The problem is that while the bank re-tried, so did the customer. And there are some customers are reporting being double-billed even though they didn’t use an iPad.

Citi says it has fixed the problem and will “replenish any fees that customers incurred because of the extra charge, refund lost interest and dole out a modest amount of points for its rewards program, called ThankYou, as an apologetic gesture.