I see this mentioned in many threads so obviously this is a known problem. I have the generator set to flat and it's still an issue. What is the real problem, and how do we go about fixing it? I'm also seeing this using the SignPortal plugin to teleport to another world. If I'm flying before using the sign I don't fall on the other side. However, I can't move around and when I leave fall mode I fall through the world and die. I'm using the head of the master branch and 0.10.0. Thanks for the input.