Wrong handling of cart rule for a free shipping configuration

[mcaporossi]

I've set a cart rule where if the total value of products in the cart is 100Chf (including tax) a free shipping should be applied to the cart. Nomally, before reaching such amount, it is correctly applied a shipping cost based on total products weight for a specific courier.

Well, the rule doesn't seems to display correctly in the cart. As you can see in the attached screenshoots if I keep adding products the cart is correctly updated but the shipping cost are not updated accordingly when I reach a total product value above the 100Chf threshold. But after I manually refresh the browser the cart rule then it is applied. Although sometimes instead of the value 0.00Chf appears, randomly, the text "Free Shipping!". The same behavior happens if I go to the Checkout procedure and add products there.

If you wanna try by yourself the web site is: www.zoyacolorfashion.ch (it's ina pre-production enevironment so do not worry to register yourself as a customer if you want to experiment)

Am I doing something wrong or is this a bug? How can this been fixed?
Thanks
Marco