Piston cannot push moss block with sign on top in certain orientations on 1.21.1 build 130+, works on vanilla

[yangyv1016]

Expected behavior

Expected behavior
Piston pushes moss block (which should break and drop) with a sign placed on top in certain orientations, same as vanilla. the Pistoncan't active

Observed/Actual behavior
Piston does not extend at all when the sign is placed on the moss block in specific orientations.
Changing the sign orientation makes it work, but vanilla does not have this restriction.

Steps to reproduce

1. Place a normal piston facing +X
2. Place moss block in front of it
3. Place a sign on top of / attached to the moss block (specific orientation: ...)
4. Power the piston
5. On Vanilla 1.21.1: moss block drops, sign drops, piston extends normally
6. On Paper 1.21.1 build 130: piston does not move at all

Paper version
This server is running Paper version git-Paper-130 (MC: 1.21.1)

Plugin list
None / clean test

Additional info

• allow-headless-pistons, allow-piston-duplication, allow-permanent-block-break-exploits do not affect this
• redstone-implementation: VANILLA in paper-world-defaults.yml
• Likely related to PistonStructureResolver attachment block scanning order / MC-188840 piston physics patch
• Video comparison: vs

Observed/Actual behavior

canwork

can not work

Steps/models to reproduce

canwork

can not work

Plugin and Datapack List

[03:10:36 INFO]: ℹ Server Plugins (67):
[03:10:36 INFO]: Paper Plugins (3):
[03:10:36 INFO]: - BKCommonLib, HuskSync, Minepacks
[03:10:36 INFO]: Bukkit Plugins (64):
[03:10:36 INFO]: - *AutoResetWorld, BanItem, BcShowItem, BCTSGuardPlugin, BetterRTP, BlockLocker, BoxedVillagers, ChestCapacity, Citizens, CMILib
[03:10:36 INFO]: CoreProtect, DecentHolograms, DeluxeMenus, dynmap, eco, EcoEnchants, Essentials, EssentialsAntiBuild, EssentialsSelectors, EssentialsSpawn
[03:10:36 INFO]: EssentialsWarpGUI, FastAsyncWorldEdit, Flyblock, GSit, HiddenArmor, Infiniteannouncements, InventoryRollbackPlus, ItemFrameProtect, ItemSoulBind, libreforge
[03:10:36 INFO]: LibsDisguises, LiftReloaded, LiteBans, LuckPerms, Maintenance, mcMMO, Multiverse-Core, NBTAPI, NoChatReports, NoChatReports
[03:10:36 INFO]: Otherside, packetevents, PlaceholderAPI, Plan, ProtocolLib, qssuite-limited, QuickShop-Hikari, RedstoneMonitor, Residence, RHLeafDecay
[03:10:36 INFO]: ScriptBlockPlus, Shopkeepers, sleep-most, StackMore, Stargate, TAB-Bridge, UserPrefix, Vault, VentureChat, ViaBackwards
[03:10:36 INFO]: ViaVersion, VoidGen, WorldGuard, XConomy

Paper version

[03:11:06 INFO]: This server is running Paper version 1.21.11-130-ver/1.21.11@c5a2736 (2026-04-11T11:14:19Z) (Implementing API version 1.21.11-R0.1-SNAPSHOT)
You are 2 version(s) behind
Download the new version at: https://papermc.io/downloads/paper

Other

No response

[mbax]

Please give this a try on the latest 26.2 build with zero plugins and datapacks. 🙂

[yangyv1016]

It works fine on 26-2, but we can't upgrade the server version. Can you provide a fix?

[mbax]

1.21.11 has been unsupported for a while. A few months ago was the time to start your upgrade to 26.1.2!

[yangyv1016]

Sorry to bother you, I tried reproducing it on 1.21.11-130 without any plugins and found it works fine! Really sorry about that! Hope you have a great day.