Damage fall-off on the Headshot Booster seems bugged; on heroes like Haze, if the enemy is afflicted by a debuff like Fixate, Headshot Booster deals 50 damage with no fall-off. Geist's Malice also causes this.
Sharpshooter is similarly bugged, randomly causing damage with no fall-off. In addition, the two seem to have a weird interaction where if you have Headshot Booster and Sharpshooter, one procs the other with no fall-off damage, depending on which item was bought first. (If Booster was purchased first, it applies the 100 damage from Sharpshooter with no fall-off.) If afflicted by a debuff like fixate, both items will proc without fall-off for 150 extra damage.
Sharpshooter is similarly bugged, randomly causing damage with no fall-off. In addition, the two seem to have a weird interaction where if you have Headshot Booster and Sharpshooter, one procs the other with no fall-off damage, depending on which item was bought first. (If Booster was purchased first, it applies the 100 damage from Sharpshooter with no fall-off.) If afflicted by a debuff like fixate, both items will proc without fall-off for 150 extra damage.