The bug

If you put a carpet on top of a piston body, extended piston arm, and slimeblock, when the piston retracts the carpet item pops out as expected, but a ghostblock of the color of the carpet on the piston body at the time appears. This is able to extend backward until the piston is no longer able to push that number of connected blocks.

How to reproduce

1. Put a horizontal sticky piston one block above any surface.
2. Put a slime block on the sticky piston's piston face.
3. Power the sticky piston from the side or bottom.
4. Put a carpet on the piston body, piston arm, and slime block.
5. Unpower the sticky piston.
6. Power the sticky piston.
7. Put a carpet on the piston arm.
8. Unpower the sticky piston.
9. Repeat steps 6-8 until the line of carpet ghost blocks no longer extends.