The bug
Moving_Block do not tick past the worldborder causing them to stay offset / create a ghost block when pushed by a piston.
This seems like a regression of MC-54366
Pistons still try to push blocks through the worldborder, however they stay at the position they were as some kind of "ghost" blocks (very likely the piston_extension block, which the client still renders, however it doesn't exist anymore, /testforblock returns air). After reloading this area they are gone.
Code analysis
Based on 1.11 decompiled using MCP 9.35 rc1
The method net.minecraft.block.BlockPistonBase.canPush(IBlockState, World, BlockPos, EnumFacing, boolean) only tests if the position of the block to move is inside the worldborder, but not if the new position is inside it as well.
The reason why the piston_extension tile entity is not removed is because the method net.minecraft.world.World.updateEntities() removes only invalid tile entities inside the worldborder.
Linked issues
is duplicated by 43
MC-280495
if yow "push" a block with a piston by the yorld border the block glitches out causing the piston head to glitch out really bad ant the block then cant be broken but also can be stood onn
Resolved
MC-271328
Piston glitches into shulker when pushing it into the world border.
Resolved
MC-271329
Block outline disappears after pushing block next/outside world border using piston
Resolved
MC-269923
Semi-blocks pushed by pistons at the border
Resolved
MC-268308
Block can't be destroyed after pushed against world border by a piston
Resolved
Attachments
Comments 16
It is not a ghost blocks. It is a "moving_block". When a piston push a block, it creates a "moving block" outside of the worldborder.
Your summary and description contradict each other.