There are multiple viewpoints on this topic, so, to clarify my own:
I am not calling for "justice", and I do not believe that anyone involved did anything that was against the law. My objection is to the attitude that it is acceptable to try to exploit the bank's mistake. What I would have liked is for people who have influence over public opinion, such as the media and politicians, to have expressed the view that such an attitude is wrong.
Some people have said that if they left money on the shop counter they shouldn't expect it to be there when they came back, or if they loaned money to people they should be certain that some won't give it back, and that it was thus the fault of the bank for trusting people and not defaulting to not allowing any money to be withdrawn when the balance couldn't be checked. This attitude saddens me. It is not wrong to expect people to behave honestly.
I also do not believe that bad behaviour by banks is relevant. Two wrongs do not make a right.