I can't say for sure.. It's $10 per person per day, so if they did.. I'd march down to the Guest Services desk and have them remove the double tip. Just because they are only one person in a cabin does not mean the wait staff is working twice as hard....If the service warrants it, then they can choose how much "more" to tip. If anything, I'd only be inclined to give the room steward something extra since the cabin is being serviced the same and he can only look forward to a single tip....
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007