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
https://www.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.
THank you