I will use hypothetical numbers, just for examples.
I have account in my bank in euros (EUR). I buy something online and pay for it with dollars (USD). Lets pretend exchange rate is 1 USD = 0.5 EUR. So when I buy something for 30 USD, I get 30 USD reserved in my bank, but stated as 15 EUR. I make a record in my book that I have spent 15 EUR.
Several days later exchange rate changes, lets pretend that it changes to 1 USD = 0.66 EUR. The same day bank fixes the transaction it has reserved earlier. Still it is 30 USD, but since the rate has changed, it fixes 20 EUR, not 15 as previously.
So the day I buy something I assume I pay 15 EUR, but later bank takes 20 EUR :(
Is such bank's behavior is a regular, or are my rights violated?