Piston TNT Duplication Glitch

Summary: By Making a 5x5 Obsidian layer with Redstone Torches on Top Then Another Obsidian Layer with 5 Piston in the Order in the Screenshot with the TNT in Middle block it has a chance of duplicating TNT.

Steps To Reproduce:
Step 1: Make 5x5 Obsidian Layer.
Step 2: Place Redstone Torches on the Layer.
Step 3: Repeat Step 1 Above The Redstone Torches.
Step 4: Place 5 Pistons as Shown in the Screenshot.
Step 5: Place TNT in Center Block.
Step 6: Repeat Until it Works.

Observed Result: Pistons Duplicate.

Expected Result: Piston Shouldn't Duplicate.