Description of the issue:

Requirements:
-Revolver and/or buzzsaw (3d weapon)
-Engieneering workbench
Tutorial how to duplicate:
1.Get desired items to copy:

2. enter the workbench & put weapon in editing window

3. quit the workbench

4.re-enter it & take the weapon with shift

5. Quit the workbench again

IMPORTANT 6. open your inventory to accept duplicated items

End. (Tested on creative mode& survival mode[works:xd:])
This glitch only occurs on singleplayer and the tool is without any modification
On multiplayer this glitch doesn't work

Versions & Modlist

forge 31.2.9 , IE [1.15.2] [0.15-105 #10] and basic, not modified modlist of the server

Crashlog after duplicating too much items and throwing them on the ground:
https://pastebin.com/7wNViTfd

I tested this (in singleplayer) and I could only actually dupe items in creative.
In survival it just gives me ghost items that go away when you click/relog/etc.
Were you testing in multiplayer?

Interestingly, the game crashes if you stop after step 4 and shift click a bunch of these ghost items in/out of the table:
https://pastebin.com/JxyCb2M8
Edit: this crash is the same as #4029