• Minecraft 1.12.2

• ComputerCraft [Build Latest Sources ?]
  You can duplicate shulkers with a turtle, it's pretty simple,

• you place a mining turtle [Normal / Advanced]

• a Shulker box with something in it, in front of the turtle

• then you do a turtle.dig()

Whats happening is that the turtle is going to have a Shulker box that is empty in his inventory and the Shulker box with the items in it, will drop on the ground

I have build the latest sources i think

This should be fixed with #560. There's a download available on cc.crzd.me. _{or you can use CC:Tweaked, which also has this fix. Just read your username. I don't feel I need to be suggesting even more forks :p.}