When you enter a nether portal in creative, you will immediately teleport to nether, and immediately teleport back, then teleport to the nether and back. You will never stop teleporting back and forth. In past versions you immediately teleport to nether when you touch a nether portal just like this snapshot, but in past versions you wouldn't teleport back to overworld without getting out and back in portal. I don't know if this happens in singleplayer, but it definitely happens on servers.