This is a link to a youtube video i uploaded about the bug might be easier to just watch this https://youtu.be/iR7PHOzUlxI

I was playing around in a completly new desert flatworld i built up with scaffolding blocks to the max built height y-256, if you right-click the top block it should add a block to the directing you're looking. This will work to it can no longer support itself so the block just falls straight off the edge, but this isnt the case. At the block where it should fall it actually placed a block and you can't continuue on any longer in the direction. If you then go back to the start and rightclick the first block that hangs of the scaffolding tower and right-click the block the block disapears and gets added to the end and it's flying in the air with no support blocks you can also just break the first or any block and it will still stand. You can keep right-clicking the block infinitely and also change directions. If you try to break the blocks in survival they do not drop this is the same if you blow them up with a tnt they still do not drop. This does not occur at y levels below 256 or 255 where the block is scaffold block is located shown in the screenshots. They also seem to disapear if i leave and rejoin the world.