It seems that this is just that, a typo. It does not appear that this was someone's idea of a practical joke.
According to the people who should know about these things, the elections office commissioners, Edward McDonagh and Larry Bugbee, a Democrat and a Republican, respectively, had the following to say:
"It's human error, it's very unfortunate, it's an embarrassment to our office, obviously," McDonough said in a later phone interview. "We wish we could turn back the clock, but we can't."The remaining ballots have been shredded. However, those that have already filled in the ballots will have them counted even though there is no Barack Osama running for President. I guess this means that everyone has agreed that Barack Osama is in fact Barack Obama.
It is indeed an interesting presidential election in the good ol' US of A.