I assumed this was because a pool of funds had been set up to prop up Romney's odds to make him appear more viable -- or at least to stave off a story that Intrade users were betting heavily against him. Intrade was a small enough market that this could have been done with a comparatively small investment compared to media buys, and without any technological or financial chicanery. It's not illegal to pay too much for something that could have been had for less.