Lava & Mineshafts

Going through the new mineshaft structures in the newest snapshot, I've noticed something....concerning. A lot of times when wandering around a Mineshaft, I've noticed it completely engulfed in flames near lava. There should be something in place to make this a rarer occurrence, otherwise, there's a good chance of finally finding a mineshaft only for half of it to be completely burnt away! At the very least it should be a rarer occurrence, ya know?