I believe that bounties that are awarded to community wiki questions should be split according to the work done by each user(See the percentages under any community wiki answer to get this data) instead of giving all to the original user. Or, the person giving the bounty can choose how to distribute the bounty manually. Feel free to add other opinions to the mix.
I agree: automatically split
This should be done by automatically splitting according to the amount of work done by each user.
I agree: manually split
This should be done by allowing the person awarding the bounty to manually choose how much goes to each user.
This should not be implemented and the behavior left as is: the person creating the answer gets all.