The cart doesnt get updated when you go to the previous page using browser back button.
So, how can you see that?
Go to your demo http://8theme.com/demo/royal/?product_cat=kids
Get into the first product and add to cart. You will see the product into your cart.
Immediately press the back button of your browser to return to the previous page.
You will see that the cart will be still zero.
THis happens with Firefox and internet explorer. Probably with other browsers but i havent tested them all.
After a couple of hours searching on that matter i found out that this is not your themes fault. It has to do with each browser. It caches the page by itself so i dont think there is nothing we can do about that. The same thing is happening on every site i tested. To conclude there is nothing you can do about that since it doesnt have to do with the theme not even with wordpress.
Anyway, please correct me if i am wrong.