I have found an issue in the latest version of the mod (minecraft version 1.12.2). In addition to messing with the game pretty badly, it can be used to duplicate items

Steps to reproduce:

1. Make a Sync clone, and place a shell storage right next to it
2. Get a pickaxe that can destroy both of them fast enough.
3. While switching, hold left click until you hear one of them break
4. Right after you hear the sound, move your mouse around erratically without letting go of left click. You should hear another thing break
5. Relog, as you've put both the mod and Minecraft in a confused state
6. Pick up the dropped items.

Here is a video demonstration
https://youtu.be/BMbKwwnXd_s

Side effects:
-After performing step 4, the game gets really confused and dropped items do not work properly until you reload the world.