Noticed this on the wiki: arrow and dart traps ignore half physical damage. From looking at the code, they call thitu() which indeed doesn't check for HPD anywhere. Except so do monsters throwing/shooting stuff at you! Checking in wizard mode (3.6.7, but the code in 3.7 looks the same), indeed, a gnome shooting +100 arrows at me does the same 100-ish damage with or without HPD. This is not game-breaking since the really bad ranged attacks are all magical, but kinda weird how nobody noticed.