When you are feeding the alf steel mana band with a dispersive spark augment, the ring never appreciates it's buffer. I went from nearly level 300 XP to almost 0 and I didn't see any change beyond what I would expect from my terrasteel armor generation. From my experience the farm I was using could fill about 2-3 terrasteel mana rings in that time, though that is an estimation.

Mod Version: 1.3.15
Forge Version: 36.1.18

Not reproducible. Are you sure its because of the greatest band of mana? have you tried to remove every other mana item (including the terrasteel armor) from your inventory?

Good call. It turns out it was my terra/alfshatterer. I wasn't aware it would try to fill the terrashatterer. Definitely not a bug.