From Dark and Darker Wiki
< . This is a Magical stat, and so will not add to sources of Physical Damage.
It does.
The reason being that Crystal Sword has its own magical damage instance. Likewise, Demon's Glee has an enchantment that creates a magical damage instance of 1.
None of your magical stats will affect the physical damage of these weapons, but they will affect the magical damage. You simply have to calculate two damage instances, one for physical and one for magical. If you use either of those weapons on a dummy in-game, you'll see two damage numbers pop up, each of those numbers is tied to a specific damage instance, one physical and one magical.