> Sounds very close to ex post facto

I don't think you have any idea what you're talking about. If a democracy can't repeal a law that's proven to be an error, you'll have quote a dysfunctional system.

Ex post facto (in the Constitution, at least) refers specifically passing a law making an action illegal and punishable after the fact. Actions can only be illegal according to the law in force at the time they were taken.

Yes. You are talking about taking people's property away with legal force because you don't like how they used it after they've agreed to buy it under different conditions.