There was a bounty on a question, but after completion of the bounty period, the half bounty was not awarded. The answer is here.
Why was the bounty not awarded?
As the FAQ says, "the highest voted answer created after the bounty started with at least 2 upvotes will be awarded half the bounty amount".
Well then why are you asking? Seriously? From the FAQ (That you already knew about):
I.e. The person that posted the bounty did not come back to award it, and the system did so automatically.
The Good News The bounty system works as designed.
Georg correctly identified that there was no qualifying criteria to allocate the bounty, also I can't find any proof that there ever was a bounty on the question at all.