Starting another knight, this time taking My Precious in character creation, attacking a door still took 3 durability, but not every time.
Starting at 60, the durability after each hit was: 57, 57, 54, 51, 48, 48, 48, 48, 48, 45, 45, 42, 39.
Either there is an issue when attacking opponents, or the drop 'every time' an opponent was hit was just a string of low rolls.
