Put the summary of the bug you're having here:
World Displaying, But not, in a sense, 'Existing'.
"Chunks where displayed, but where a 'ghost' of what should be there."

What I expected to happen was...:
Describe what you thought should happen here:
"What I Expected was for the world to load, and be able to use the command_block s I had used prior to the error."

What actually happened was...:
Describe what happened here:
"The world was displayed, however the chunks where acting like ghost blocks and when leaving Creative fly mode I slowly sunk throe the ground as if I had walked into a chunk error like what you got in beta, But the only difference was, it displayed a chunk where I was falling throe"

Proof that the error indeed happend:
(https://www.youtube.com/watch?v=eAYI9Q7lir4)

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
"1). I started recording to show how to setup Minecraft 1.9pre15w42a
2). I loaded up a world that I had made in 1.9 snapshot 15w42a
3). I attempted to open the command_block interface
4). Nothing Happened.
5). I checked to see that I wasn't in Spectator mode.
6). I was Indeed in Creative
7). Then I tried to land on the command_block
8). I landed on it, and proceeded to slowly fall throe the command_block
Into the ground, as if I where in a Beta Chunk error.
9). I Logged off. Then Stopped my recorder. "