"If it's about the extra jar file named "ImmersiveEngineering-[version]-core":
This is intentional. It's Forge convention to make Coremods into a seperate thing. This jar is not an unauthorized download, it is shipped with IE and automatically unpacked by Forge."

What about this folder then?
"mods\memory_repo\blusunrize\ImmersiveEngineering-core\0.12-81"

That's the same thing but better. You are using a very new Forge build (later than recommended). Up to now you had to delete the old core jar to prevent both versions of IE core from being loaded. Forge recently added this memory repo system that prevents this issue.
I'll keep this issue open as a reminder for me (or Blu) to add info on the memory repo to the paragraph you quoted.