I was experimenting with the new uses of /setblock when i came to the piston extension. So i used 33:0, 33:1, 33:2 until i got to 33:6. This block is completely transparent and has no crash barrier (I think that's what it is called). However when a block update happens to it or adjacent to it the world crashes. Further, the world crashes when Minecraft attempts to destroy the block (TNT, Creative deleting). I experimented with the block and TNT will destroy the block AFTER minecraft crashes. And when I tried to run it through MCedit,it would not load. I am aware that this is not a large problem however I feel the need to report it anyway.