How it should work: If you are wearing no weapons and try to wear one, it will stick it in your main weapon slot. If you are wearing one weapon and try to wear another weapon, if you don't know dual wield or if the weapon is not suitable to be dual wielded, it will try to replace your main weaponwith the new weapon...otherwise it will attempt to dual wield it. If you are already wearing two weapons, if the weapon is suitable for dual wield, it will try to stick it in that slot, otherwise, it will try to stick it in your main weapon slot.

Try the paragraph above. Few things:

You cannot wear weapons.

IIRC dual wield doesn't replace main wield, it's just a too heavy-message.(correct me if I'm wrong here)

This looks like how dual wield worked before you started revamping it.