I was playing Minecraft with others. Someone wanted to play on one of my adventure worlds, that I had created in Creative. I opened the world to LAN, and someone joined my world using "Direct Connect". After that person joined, I wanted to edit a command block. However, when I right-clicked on it, the command block would not allow me to edit it, but instead reacted like a block that cannot store data, such as stone. I was still able to edit the block with "/blockdata", and I could receive and place command blocks with pick-block and "/give", but I could not edit the command block the normal way. I was in Creative when I attempted to edit the command block. This also happened several other times. The world was created in version 1.9.0.

strong What I expected to happen was...:
I expected to be able to edit the command block by right-clicking on it in Creative.

strong What happened was...:
The block reacted in the same way as a block that cannot store data, like stone. I had to edit the command block by using "/blockdata" from the chat line.

strong Steps to Reproduce:

1. Create a World
2. Place a Command Block
3. Save and Quit to Title
4. Re-Open the World
   strong # IMPORTANT Do NOT Edit a Command Block by right-clicking on it.
5. Open the World to LAN; The Game Mode Does Not Matter, But Cheats Have to be OFF
6. Right-Click the Command Block, and Wonder How to Fix This
7. Save and Quit to Title
8. (Sometimes) Watch Minecraft Become Unresponsive

I have attached a copy of the Game Output of a world called "Test Bug" to this bug report. This bug sometimes makes Minecraft unresponsive as well. This bug can be avoided two ways; you can either right-click a command block before opening a world to LAN, or you can open the world to LAN with cheats enabled. Thank you for your time.