Personality traits change before spells are actually cast, so right now a cast spell affects dominant traits/imbalance for its own cost calculations. I feel like the intended working here is for personality traits to be checked at the start of the round, as otherwise casting a spell with a trait not strictly lower than your highest will make that trait dominant immediately for that same round.

EDIT: previous wording was ambiguous depending on whether “selecting” can be done multiple times, this should be more scamproof.