It's common. Lloyds once charged me overdraft fees twice when I left England and my last debit came before my landlord returned my garanty. They then kept charging me fees for a sub-zero account every month for three months while my account was in the green before finally charging me overdraft fees triggered by their own mistake.

They didn't refund me everything once I pointed it. I'm fairly certain they did it on purpose hoping to siphon out an account with little use.

Banks are shameless.