I Don't Die When Falling Through The Bottom of My Worlds.

In a flat world, in creative, difficulty turned off, all fancy graphics and render distance on fully, I dug down to the bottom of the world and fell down through the hole. Instead of dying and beeing given the option to respawn, I just fall and land on some sort of completely invisible platform that extends forever underneath the world. If you look up, you see what appears to be the underneath of the flat world.I can then fly back up and come out on top... Weird.... In the screen shot the yellow stained clay is where I dug throug, and I am standing on top of an invisible platform.