These were caused in a 1.2 glitch when a piston was pushed by a piston. They can be used as shipping crates. Now, we can obtain these with mcedit or other editing programs. We can also get them by loading a world in 1.2 or lower(be sure there are still pistons) and push a piston with a piston. Setblock commands can also place these blocks, allowing for a reset button on an adventure map featuring opening crates to get items (with a lever in front to open)