After equipping a gold sword and using it, it continues to lose durability and is destroyed even after not being equipped. I have lost three gold swords in this manner, so its no fluke. I don’t think its being used (adding to attack) after being unequipped, I think its just losing durability as if it is being used. I will try to pay more attention to this issue in the future, but gold swords aren’t exactly a dime a dozen.
I think this is due to crafting. Most crafts require a Sharpened Item, in which it’s using your Gold Swords for. To prevent this from happening (for now), place the Gold Swords in a Small Bag/Backpack in your inventory.
It would be neat if there were tool slots, which let you set specific tools for crafting, or require you to set the proper tools for a crafting recipe. It could also be used to exclude different items of the same type for a recipe, in case you want them in a different recipe.