You used to be able to place a piston_head with damage value 6, and make it invisible so you couldn't open dispensers or chests. Then, piston_head 6 got the missing texture, even tho it is a invissible transparant block. Now, when you try to place a piston_head, you get the error message "An unknown error occurred while attempting to perform this command". Bring back piston_head:6 and piston_extension! We want to make awesome adventure maps!