Problem:

Two vertically stacked pistons pointing downward, connected by Redstone on top, behave differently depending on certain coordinates/diagonals. Most of the time, the upper piston extends and pushes the lower piston down. However, at certain coordinates, only the lower piston extends instead.

Observations:

• There are noticeable patterns in this behavior. When you find a spot where the lower piston extends, the same behavior repeats approximately every 16 blocks.
• In the x-z plane, this behavior follows a diagonal line: On one of the two possible diagonals, the same behavior occurs consistently.
• Changing the height also shifts the spots where this behavior happens, but the pattern remains.

Consistency:

• The behavior is consistent when toggling the Redstone on and off.
• These patterns occur both in a Survival world and in a Flat world (see attached images).
• The issue was tested in Minecraft versions 1.21.1 and 24w40a, and the behavior was consistent in both versions.

Expected Behavior:

The same piston (either the upper or lower) should always extend when Redstone is powered, regardless of the coordinates.

To reproduce it:

You can execute the following commands on a default superflat world in creative mode:

/execute in minecraft:overworld run tp @s 12 -56 18 90 30

/fill 8 -58 21 8 -58 14 minecraft:piston[facing=down]
/fill 8 -57 21 8 -57 14 minecraft:sticky_piston[facing=down]
/fill 8 -56 21 8 -56 14 minecraft:redstone_wire

/setblock 7 -57 18 minecraft:stone
/setblock 7 -56 18 minecraft:lever[face=floor,powered=true]

There should be a spot (8 -56 15) where the lower piston is extended instead of the upper