(This also applies to Headshot Booster and Weakening Headshot.)
If you buy the resist reduction item before the headshot item, then a headshot will apply the resist reduction before the bonus damage, so you will deal more damage.
If you buy the headshot item before the resist reduction item, then a headshot will apply the bonus damage before the resist reduction, so you will deal less damage.
Expected behavior: Buy order shouldn't matter; you should consistently get the same result (ideally the more favorable one so that it doesn't feel like an arbitrarily missed opportunity for item synergy).
If you buy the resist reduction item before the headshot item, then a headshot will apply the resist reduction before the bonus damage, so you will deal more damage.
If you buy the headshot item before the resist reduction item, then a headshot will apply the bonus damage before the resist reduction, so you will deal less damage.
Expected behavior: Buy order shouldn't matter; you should consistently get the same result (ideally the more favorable one so that it doesn't feel like an arbitrarily missed opportunity for item synergy).
