The exact same thing happened to me - I sailed on the Golden Princess which left on 22 December, and I put some on board credit on and it showed as $139.10, so I called Princess and they had a look at the booking and they could only see the correct amount of the $125.00. They had no explanation for it. So I checked my credit card and it went through as the $125.00 (Aussie dollars). Once on-board I checked what credit I had and it was the $125.00. So it must be a glitch in their system somehwere.