So I launched my “Just GT6 and NEI” Pack, and it has the same Potion Bottle Metadata that my normal Test Pack has, so whatever it is, it is caused by some other Mod…
What makes me very suspicious is that the Metadata values you told me about are identical to the ones Et Futurum uses for its lingering Potion Item, so something must be messing with it, and weirdly enough it is NOT Et Futurum (despite them using the same “wrong” metadata) because I do have it in my normal Test Pack too…