Its not a matter of the Level generator sucking, its a matter of you sucking
its the level generator
it'd make no sense to light a fire underground and magically have the ground above you collapse upon you
it happened once with sand, I was just walking on the sand and there was a cavern underneith
somehow, something made the sand fall directly in to the cavern underneith, and it wasn't me, and it wasn't any creeps.
the level generator is stufftily done, because it creates gravity-defying landmasses and sets things up to defy its own physics.