Flood barrier cannot be bought by cash, but can be bought by faith. And dependless of how many tiles are affected by rising sea level - the cost is always the same and is insanely cheap. Who cares 8 tiles being flooded, just send envoys to Valetta and buy a barrier for... 160 faith. And compare the cost to the cost of missionairy.... I always thought someone noticed so such a gamebreaking bug should be fixed now. And still after new patch it is possible.