Placing a door infront of an extanding piston at the exact right moment makes the door into an invisble block.

Update*

• It is no longer becoming a invisible block, now it becomes a half door (Top door)

Recreate:

1. Make somewhat what I did in the pictures below.
2. Jump onto one of the pressure plates and place a door infront of the piston just before landing on the pressure plate
3. If the door just pops out and dropping a door, try again untill you hit the right timing

There is a short video showing how in the following dropbox link:

https://www.dropbox.com/s/novo4o8xkhi1ptp/javaw%202014-02-14%2021-54-50-70.avi

Thinks i tested about it:

• Mobs can walk through the invisible block.
• Right clicking the invisible block makes is disappear.
• Right clicking somewhere else with the same slot as you held the, places the door.
• the invisible block acts differently which way it is pointing.
• placing a pressure plate below the block makes the block sometimes act like a regular door, but still invisible.
• standing on the invisible block with a pressure plate below yourself, activetes the pressure plate once in a while.