I recently made a 500 reputation bounty on this question. As I was really interested in getting an answer I crossposted it on MathOverflow. On MathOverflow I got an answer and for completeness reasons I copied that answer on MathStackexchange. This answer got several upvotes but it remained the only one. So the bounty expired and noone got the reputation.
In the description on the privilege it says
If you do not award the bounty within 24 hours of the bounty period ending, half the bounty value will be automatically awarded to the top voted answer posted after the bounty start, provided it has a score of at least 2.
Maybe this should be modified and the information added, that this is not rewarded to the OP. Another question is what happens when there is a answer from the OP with for example 4 upvotes and another answer with 2 upvotes. Will the second most upvoted answer receive half of the bounty?
Please note that I really think it is important that you can't manually award the bounty to yourself.