https://www.youtube.com/watch?v=piKRlgIfjcU&feature=youtu.be

The video explains it all except for one little thing. This only happens when you open a bag of the same size (color doesn't matter).

EE3 version is 0.1.140

Thanks for quick response! It even makes sense for me and I'm not a developer.

I can reproduce this, but only when copying the alchemical bag by 'middle-clicking' in creative. This makes sense because the UUID will also be copied and so the wrong ItemStack can be found (it will find the first in the players inventory).

That makes perfect sense - guess I'll have to watch for that event (the copying of the itemstack in creative) and regen the UUID at that point