This is not a bug but i would call it a game mechanics problem... I was putting in a boat mine entrance today on my deed and i discovered the hard way that i could surface mine two dirt/slope lower than the game allows us to tunnel in water. Luckily I could still use concrete to get the tile back high enough to be allowed to tunnel again but if not i would have been really upset right now, lol edit: I guess it should be either reversed or made to be the same height so others do not run into this problem.