Using two observer blocks with inputs facing each other to power a sticky piston causes the piston to extend once per tick, and retract once per tick. Placing slime blocks above the piston to create an "L" shape, then breaking the corner, causes the slime block outside of the 1x1 area to be grabbed, during which, the client does not seem to update properly, and for a few ticks, a temporary "ghost block" is created, before being immediately updated, and removed. This seems to affect all three axes, with no regard for whether the machine is facing north/south or east/west.