CTRL-Clicking any machine upgrade while they're in a Modern Industrialization machine will duplicate them.

I'd show a gif illustrating this, but I think this works just as well...

I regret nothing.

A part of me genuinely isn't sure if this is a bug with the modpack or Modern Industrialization - but I refuse to believe I'm the first one to find this.
Unless this can be replicated easily by other users (which I know it may be) then there's a chance this is just a strange issue with my friends server.

does this happen without InventoryEssentials

Same duplication when Ctrl-click on items in the MI Configurable Chest.

Upd
Tested this without InventoryEssentials, and problem fixed... because now Ctrl-click do nothing.😁

This has been fixed as of 1.4.4.