Bow Attack Firing 2 Addition Arrow On Dualstring Bow (Bugged?) Deadeye POE2

My Ascended Deadeye friend picked up a Expert Dualstring Bow with a "Bow Attacks fire 2 additional Arrows" roll, upon firing his new weapon i think it may be bugged?

In Theory one should be firing 5 arrows, however my friend is shooting only 4

Bow Attacks fire # additional Arrows
Endless Munition = 1 Arrow
Dualstring Bow (Implicit) = 1 Arrow
Dualstring Bow (Roll) = 2 Arrows

Skill Attack = 1 Arrow

Total = 5 Arrows

Does anyone know if this is intended or bugged?

i have 4 arrows and i have dualstring bow but it seems it doesnt add additional arrow for some reason, i noticed that only now too