If you run Naxxramas and clear wing X, use the teleporter and then go back up the same wing X, you’ll trigger some kind of teleport animation as soon as you get within a certain range of the teleporter. This range goes beyond walls (in the military wing the animation triggers just past the first boss because that ‘just’ clips into the range) and beyond wings (the animation triggers for the plague ward if you get too close to the boss room while in the spider wing). It is also not a border, but rather a field: trying to sneak/teleport past it will still trigger the animation. Several fields can be up at the same time as demonstrated by ‘priming’ the spider wing and the plague wing. If you then run the spider wing again you’ll trigger the animation in the cavern just before the second boss (for the spider wing) and in the corridor just before the outer ring (for thr plague ward). There does not seek to be a possible sequence of wings that has any effrect on this effect.
So far ive been unable to find out anything useful regarding why this happens. I would love the input of the forum whether this is a possible secret or just an old glitch.