I think that might be refering to the new magic weapons like the dualing swords that is actualy a pair of weapons so you get an extra attack but you can't use your shield.
If your refering to page 501 where it states that if a character has two magic weapons they have to declare which magic weapon they are using and must use that magic weapon for the duration of the combat. Your still mistaken. On page 500 of the BRB it clearly states that you can not take more than one item of each type (weapon, armour, enchanted etc). But states that there are some special characters whom have more than one magical weapon and it's assumed there is some safety measure built into the magical enchantment that allows them to carry them simultaneously.