But the size of the charge, typically two dollars, didn't change. All of the economic models - including the Reserve Bank's own model - suggested we would use ATMs pretty much as we had before. The incentives were much as they had been.

Instead withdrawals from foreign machines dived from around half of all ATM withdrawals to just 40 per cent. Among senior citizens the proportion fell to less than 10 per cent. The group the Reserve Bank had thought would be the least able to shop around turned out to be the keenest to drive across entire suburbs to avoid the two-dollar charge.

A Reserve Bank study released yesterday says it's behaviour that ''cannot be accounted for by the model of ATM fees presented in this or any other existing paper''.

To work out why, it has turned to research on retailing and a finding that point-of-sale displays can change purchasing decisions even when they convey no new information.

It says one of the reforms it introduced in 2009 was effectively a ''point-of-sale prompt''. Since then every foreign user attempting to complete a transaction has been presented with a message reminding them of the fee and asking them to press a button to either continue or cancel. An astonishing 10 per cent of us confess to cancelling at least once in the past month.