Duplication Bug of the Forcefield Controller
When you have one forcefield already placed and try to make another one that crosses the existing one, the Forcefield Controller duplicates itself in inventory. Can be done again and again.
It is very easy to exploit and has a 100% repro-rate.

Versions:
Minecraft 1.12.2
malisiscore-1.12.2-6.5.1
malisisdoors-1.12.2-7.3.0

Only these two mods are installed. Tested on different forge versions.

Can confirm MalisisDoor Forcefield duplication glitch. A secondary problem with this glitch is if the original controller used to create the first forcefield is discarded the forcefield cannot be removed.

Versions:
Minecraft 1.12.2
malisiscore-1.12.2-6.5.1
malisisdoors-1.12.2-7.3.0