Janna's Whirlwind

Currently, on the public servers, when you cast Janna's Whirlwind with enough mana, but casting it put's you below the mana cost, the ability will not allow you to immediately use it to send it out early, up to a whole second. This is a big problem for early game Janna, because that gap in cast time is time your enemy can use to get around it. Riot, if there is any way to fix this, because it is a trade/engage/disengage impacting spell, please do.