Enemies with the Fire Immunity buff are also improperly immune to the piercing damage when shot by the Dragon's Dowry Arquebus.
I'm not talking about enemies with "Immune" as their listed amount of Fire armor, these enemies will still properly take the piercing damage. Enemies with the Fire Immunity buff are completely unaffected by shots with Dragon's Dowry, presumably because it does a small portion of its damage as fire.
When shot with the weapon a popup flashes that they are Immune, and the entire shot has no effect on them.
This is in v4.1.2.0047.