A bit fair at BetFair

Remember my bet on Cameron to be nominated? You'd think I'd be happy - but Betfair altered the rules slightly to reflect the new nomination process and have decided that...based on the old rules, Cameron wouldn't have been nominated and so I lose my bet. It's a bad call from them, my bet was placed knowing that more than two people might be nominated by whatever process - I'm a bit miffed at their decision. Some other punter wins though, and is probably laughing. Is it fair? It's a bit Fair.