So, I was playing a game as Anivia using the new manaflow band because MANA YES.
After the first use of my ultimate...
Manaflow band stopped stacking at 150 mana.
Maybe it has something to do with toggable ults, but it was pretty annoying, since it happened right after I reached level 6.
I dunno, I just needed to point this out since it was pretty big.