There is a good thread on this issue on cruise critic I suggest you read it. A poster from the banking industry gave the clearest answer I have ever received on this subject. If your credit card is affiliated with one of the banks he mentions please be aware that this may happen to you. We have always been able to get the charges reimbursed by Regent and Oceania and it is happening less but I still think this is great information. Very few people hit this problem but it does happen.

http://boards.cruisecritic.com/showthread.php?t=812463