If you have “reset equipment” ticked in the options, it works if (e.g.) you switch from one single item to another single item (e.g. from crossbow to sword) during the course of battle, but it doesn’t work if (e.g.) you switch from a 2H item (e.g. crossbow) to two separate items (e.g. sword+shield).
i met a similar situation:
when my archer switch his bow to fail and shield, after battle, his weapon wont be reset,
but if he enter the battle with fail and shield while, during the battle he switch them to his bow, after battle, his weapon will be reset.