The way it seems to work is that the only time the game cares about your facing when using abilities is when you start the cast, and end the cast, anything during the cast time the game doesn't bother to check if you're still facing the right direction. This is also why the game will continue to let spells be casted when the target is dead, but ends up failing to cast because, well, there's no valid target when the game goes to check if the cast is successful, it doesn't care about whether it's valid or not in the middle of casting, only when it starts or ends.

I don't bother with the technique honestly, the only time it's relevant is during look-away mechanics, and I'd rather burn an instant cast spell to resolve it than switch to Standard controls.