I rarely had it happen in MoP (Maybe 2-3 times through the entire tier of raids), but BRF seems to be a glitch farm for my leap. I've had issues with in on blackhand, maidens, thogar, and furnace. Nothing like going for that leap to the door w/a bomb, dcing instantly and detonating on top of the tank/melee...
I've always called this a terrain DC since it became a thing sometime around the beginning of cata when they changed how terrain code works to keep players from bugging out of certain areas. It happens with any class that has abilities that lets them move extra distance, instantly or not. Warrior charge and mage blink have historically been some of the most buggy spells in the game, allowing you to fall through the world in certain terrain seams since launch to this day. I've fallen through the ground with Demo leap as well. You can also get 'Terrain DC'd' by standing under the elevators in BRF and jumping up at the same time as the elevator is coming down as it hits you the head.
This happened to me for the first time ever on Hans and Franz last week. I thought for sure I would be dead when I came back, but phew - lucky me - the press phase was over and I was still on my feet. I don't think on it too much, I mean I've been using it for a while now and only DCed once, but if it happened more often I would, for sure, find it annoying.
it happens to me aswell as when i STRAFE my camera with my mouse too fast in walls or corners makes me instantly DC i cant even do arenas in nagrand without dcing if i just move my camera with my mouse rly fast...
i had just noticed this thread before going farming wednesday.. Lo and behold, super dps on flamebender, leap in for firestorm, Rip. Never noticed it as a problem before..