"In 2005, Dr. Zhang was having an ongoing discussion with friends about the Lottery, with Dr. Zhang taking the view that it offered poor odds and was a tax mainly on poor people. To bolster his argument, he began analyzing the Massachusetts Lottery’s various games. But when he got to Cash WinFall, he was shocked to find that during roll-down drawings the odds were in the bettor’s favor."
Full story here - it's rather engrossing.
http://www.mass.gov/ig/publications/reports-and-recommendations/2012/lottery-cash-winfall-letter-july-2012.pdf
It may be that the state is 'skimming' the rolled over funds from one jackpot to the next: imagine jackpot #1 is short $100 of being +EV, and $50 is kept by the state and $50 is rolled over to the second, which is now short $50; the second jackpot also goes unwon, so another $100 is split between the state and jackpot #3, and now jackpot #3 is neutral EV. Anyone who entered jackpots #1 and #2 lost money, while those entering #3 neither lose nor gain on average, and if there is a jackpot #4 (because again no one happened to win #3), then those entering #4 can expect to gain money, while the state is now up $150. If you follow me.