You could even argue that a flag type 3 is warranted but only if raised by a participant, I mean, if I was told that if I participate and do a,b,c I could win some x prize, and after that you decide that you no longer want to give me my potential prize,  you have certainly violated a contract.

Such actions should be frowned upon, or else, someone can start a thread saying they will give away 10 btc for the winner, gets a ton of merit for being generous to the community, and then a few weeks before payment time, they pull the plug.