Duplicating sticky pistons

I was playing with redsone, 1 tick timer and sticky pistons, when I put a block (sandstone, but with others it's the same issue...) between two pistons
facing each other. I figured that should break the mechanism, and stop the piston noise, but...

That duplicated the pistons !!

(I was turned to the west, I don't know if it works in other directions...)

To do this again :

1. Create a 1 tick clock with two repeters, powering 2 blocks.
2. Place 2 sticky pistons along these two blocks, face to face.
3. Turn your clock ON.
4. It's the more difficult because of the rapidity : place a block between the two pistons !

Thank you for reading me, and sorry for my english... I'm French ! ^^