modifyDamage{mode=ADD} adds the incorrect amount of damage

Found some weird behavior with the modifyDamage mechanic.

For some reason on ADD mode, the damage added is Attack Damage * amount, not just the amount defined.

Example Item used:

the_stick:
  Id: STICK
  Display: The Stick
  Attributes:
    MainHand:
      AttackDamage: 10 
  Skills:
  - skill{sync=true;s=[ 
    - message{m=HIT} 
    - modifyDamage{a=1;action=ADD}
    ]} @self ~onAttack
  
the_stick-control:
  Id: STICK
  Display: The Control Stick
  Attributes:
    MainHand:
      AttackDamage: 10 

The Stick should deal 12 damage (10+1+1), the Control Stick should deal 11 damage. Instead The Stick deals 21 Damage, (10+10*1+1).

Damage instances from skills work as intended, just not ones from the ~onAttack trigger.

Demoed here: https://youtu.be/KOgv2XXslHI