For the two melee weapon careers, Slayer, Grail Knight, and Warrior Priest, applying a new skin to the weapon in Melee-Ranged slot via the Overview menu in the new UI bugs out. As a consequence it unequips the current primary melee weapon and replaces it with the exact same weapon the player just applied the new skin to.
And some screenshots on the old UI to show it really is the same weapon equipped in both slots. Which normally is not allowed.