Added protection for the Piston/Item Frame dupe glitch present in Spigot 1.12.2 final (and possibly below) as long as you're running a recent version of 1.13 this should be patched.

The way this dupe works is players place an item frame on a piston with the item they wish to dupe, (including full shulkers). They then extend/retract the piston and time punching the item frame correctly resulting in a dupe drop.

Whenever this dupe is detected the location of the offense as well as the item that was attempted to be duped is logged to the console.

Video example


There are a couple other variations of this dupe including using a retraction with a sticky piston on another block but version 1.5 should cover all variations of this dupe.