You can create pistons with two piston heads

When a piston is placed by a player who then turns their head away before the server registers the placement, a second piston head will visually appear extending from a different side of the piston. This piston head is only the result of a client-server desync, since right-clicking on it or saving and reloading the world makes it disappear.

How to reproduce:

This is the most consistent way I've found to reproduce this issue. A video of these steps is attached below: MC-254385.mp4

1. Place a redstone block.
2. Position yourself one block diagonally away from the redstone block.
3. Give yourself a piston.
4. Run the command:

   /tick rate 1

5. Rotate the camera so that you are looking at the redstone block at an angle of exactly 45, 135, -135 or -45 degrees.
6. Turn slightly to your left (or right).
7. Right-click with your piston on the redstone block and quickly turn slightly to the right (or left, respectively) of the diagonal you were previously facing.
   → The piston grows two heads.

Expected result:

A piston with one piston head would be normally placed.

Observed result:

A piston with two piston heads facing different directions was placed.