I have alternate cast bound to mouse scroll up and mouse scroll down. For any instant/quick cast ability, scrolling the mouse does not trigger the alternate cast prompt or trigger the alternate cast when used with the skill. The use case that this is affecting for me is Doorman's Luggage Cart...
I think this is actually an issue with the increase not being displayed because it's conditional or something. I just tested it out with Celeste, and even though the change wasn't reflected in Spirit Stats or the ability description, her Radiant Daggers circle is visibly larger with 16 stacks.
Bumping this, found the same thing happened when enemy Shiv bought Frenzy. I watched the replay and he actually has Hunter's Aura in that flex slot.
Match ID: 22916768