The Bug

observers reading blocks getting pulled are locational, meaning the update order from observers is not reliable in specific cases. Moving over the setup in the attached image with /say 1, say 2, and say 3 in the command blocks.

Steps to Reproduce

• Build the setup shown in the image.
• Set the command blocks to /say 1, /say 2, and /say 3.
• Activate the piston and note the order that the numbers are said.
• Test in multiple locations and note the differences.

Observed Behavior

The order of numbers differs based on location, this is due to the piston code that reads from a hash map when removing leftover blocks after creating moving blocks.

Expected Behavior

The order would always be the same, thus being predicable and reliable.