Bukkit

What steps will reproduce the problem?
1. Place protection block.
2. Push block with piston.
3. Use command /ps unhide.

What is the expected output? What do you see instead?
Expected: Block to appear where initially placed.  This is exactly what happens though. The pushed block still exists as well, so this allows for the duplication of protection blocks.

What version of the product are you using?
ProtectionStones1.8h

Do you have an error log of what happened?
No. Not an error.

Please provide any additional information below.
The working fix we have is to set the protection stones immovable with in-house plugin.
I've attached (hopefully) the file with that plugin/source code in case you would like to use it.

This is not a defect but a known limit of WorldGuard's Protection against piston attacks and has been noted on this plugin over and over again since the oldest versions of PS.

That is why I added the ability to set PS's to auto-hide, and block players from using the "/ps unhide" command then they can use the "/ps reclaim" command to get a PS back and remove the region.

As a note the newest versions of WG do finally have a piston flag, but this would stop pistons in a region, and would protect from piston attacks outside a region, but this wouldn't allow the player to use them at all. And this still wouldn't protect your server from the region owner purposely duplicating PS's.

And for PS to monitor all PS locations would not only require it's own database but would also put a load on a server to protect all those blocks.

I did see that several plugins now allow a list of blocks that pistons can't move.

For example adding this line to Essentials config.yml would block the id's listed.

piston: 4,64,324,98