Update Cart with Ajax – left to free shipping is not update

Hello,
i hava already installed the Booster Plus. i want to show my users the option, how much they needed till free shipping.
i show the message in the cart – but when i update my cart (quantity of a product) – the left_to_free_shipping does no update…

how can i fix that problem?
i want that i can make an update at my cart – the left_to_free_shipping do it also…

Best Regards,
Ben