[sire404]

No it's most likely just overconfidence in the market by a few individuals.

Intrade actually checked for manipulation themselves:

"We checked this out for potential manipulation - it certainly fit the pattern at first glance. However, during the period you reference above 40 individuals bought Romney shares and no individual bought more than 15% of the shares traded during that period. A look at those 40 accounts shows nothing suspicious. So we don't believe this was manipulation but more a run on Romney when the market was unusually thin."

http://www.theatlantic.com/business/archive/2012/10/should-p...

However, even without this spike the Intrade market was misaligned for more than 24 hours. A few of our arbitrage customers made huge amounts of money (outside our software) trading 5-10% arbs between Intrade and Matchbook. This is extremely uncommon.

Disclaimer: I'm one of the developers behind sports arbitrage software RebelBetting (http://www.rebelbetting.com)