I believe that the Apollo businesses all use this Irish Bank. I am sure there is some big financial reason to do this. Regent and Oceania therefore as part of the Apollo companies have to bank with this bank. All transactions are done in US dollars so the charge should not be made by the credit card companies.
Most credit cards adapt pretty quickly and stop charging the fee that is not really applicable since no foreign transaction took place.
Initially it was a real mess with this happening to a huge number of people. Now it is very rare that this occurs. If it does occur and the credit card company will not remove the charge the cruise lines will refund the fee.
It is a real mess though and time consuming for both the passenger and for the travel agent as well.