The storage matter extractor can be used to duplicate items, when two people look into a extractor and insert items that aren't storage containers, they will be added to both players inventorys. Its also possible to put an item in and quickly pull it back out to duplicate it.

I found this glitch in multiplayer on a server in case that has anything to do with it, the server runs this collection of mods, although i don't think its caused by any other mod.