Beneficial mutations increase in frequency over time. In this case, the gene has gone from one individual to 33. Beneficial mutations, almost as a rule, don't decrease. If a mutation goes from lots of people, to one person or less, by definition, that's not a beneficial mutation. Selection doesn't select like that.
Faith did point out that there may be very little selection on this allele since it might not affect anyone until after reproductive age.
Also the increase in the number of people carying the gene may reflect nothing more then the increase in overall population that happened last two centuries. I think crashfrog is right to believe that this is a case of benefical mutation but I don't blame Faith for feeling the need for a little more convincing evidence. Unadvertedly, though, Faith is making another point which is that even if it is a true case of benefical mutation, that is not easy to prove. Therefore the fact that not many cases of benefical mutations have been found so far cannot be taken as evidence that they do not exist or are to rare to be relevant, because it is so hard to prove that you have one (even when you are staring at one).