Yeah I found this glitch on my own too all you need is a verticle ledge and a yeti and you can push yourself past the border and end up on the other side. Now my theory is the game thinks you are still on the layer you were previously on, it uses stairs to know when you are on one level or another.
So you are basically moving on a layer below the layer you are walking on and that's why there aren't a lot of boarders and you can walk on air. It's a out of bounds based on which layer the game thinks you are on. If you move near stairs or a legit way to get down or up a layer, the effect will be gone.