Blocks pushed into border become invisible, indestructible when the piston is broken, and persist after reload

When pushing movable blocks into the world border using pistons, they become glitched and persist invisibility after a world reload or shutdown. these phantom blocks retain collision, cannot be broken or detected using commands, f3, and creative mode, and swallow falling blocks entirely without dropping items or creating entities.

steps to reproduce.

1. Get a Redstone ready superflat world

2. Teleport to X = 29999983

3. Place a movable block at the edge of the world border

4. Place a piston facing eastwards behind the movable block

5. Power the piston to push the block (should cause the piston to clip inside the block)

6. Destroy the piston whilst it is still powered

7. Save and reload the world

afterwards the block becomes invisible and undetectable, and it retains collision (pushing mobs and players)

cannot be removed using /fill, /Setblock, /data get block, and breaking in creative. does not appear in the f3 debug screen. it persists across saves and reloads. If a falling block (like sand, or anvils) lands on the glitched block, it is deleted completely (sometimes drops as an item) and if the piston glitch happens with sand. the sand remains in the air and becomes invisible after reloading

Tested in Java Edition 1.21.7 on a Singleplayer Redstone Ready Flat World, with no mods, or plugins

This allows players to:

• Create unbreakable invisible blocks

• Delete falling blocks

• Break expected behavior of piston and gravity-based mechanics

• Potentially grief or damage multiplayer servers if not patched