This makes it annoying to filter empty tablets, as you have to filter on both empty and freshly crafted tablets. I believe this probably has something to do with nbt tags not being set on crafting. (Botania 228)

I don't get what the issue is.

i think what he wanted to state was, an freshly crafted (thereby empty) mana tablet is not the same item like an "used" empty mana tablet which makes it hard to setup filter for (i did not check if this is true)