Quinn ult

Birds ain't got hands.

That's not a bug. The use of MOST summoner spells, and quinn's other abilities other than W will take you out of her out of her ult, and force the use of Skystrike majority of the time. If you flash while riding Valor, you will no longer be on valor. If you use Ignite, you...yea you get the point.

Heal, Cleanse, and Barrier will not force quinn off valor. Getting attacked by neutral monsters, turrets, and other players will force you off Valor. (Minions only slow you down, A LOT)

To better explain the Snow ball issue to you... You're attacking (and marking) your opponent and this is considered a standard attack.