Version 2.11b--1.12.2 From the Modular Mayhem modpack. Alloy Furnace duplicates itself on place.

From here: https://www.youtube.com/watch?v=5NiNqWH7lWQ

At time 8:30

Never mind. On closer inspection, I think he simply made another somewhere along the way. Trying to verify, I'll getre-open if I can get verification

Yeh, he just had another one in his inventory and inventory tweaks moved it to his hot bar after placing the first one ;)

I caught that on second viewing. Sorry about that.

No prob!