I was laying Minecart Track in a superflat world when I came across an area of blocks that looked like farmland, but it was not. On the top texture of the block, text read "UPDATE." I went into survival mode and mined a couple different blocks in different areas, but they were all the same thing. I went into the inventory and hovered over the block with the cursor. The block name was "tile.info_update.name."

How I think you can reproduce:

1. start superflat world in peaceful mode with cheats on and trust player permissions on operator. Multiplayer set to Friends of Friends and LAN Game ON.

2. lay powered rail in a straight line.

3. If that doesn't work, try to do it in a different direction.

Sorry I can't attach a picture, I was playing on my friend's tablet.