This is related to issue 1291, but instead of the book cast, it is about the regular cast (Z).
As far as I know pressing 'Z' is the only way to investigate your spells (apart from remembering them), so it seems a bit unfair that the monsters are already hitting you when you decide that spell casting currently is not your best option.
And it certainly is not consistent with many other areas in the game where cancelling an action does *not* take a turn.