The problem is caused by woocommerce notification function.
If you don't leave the page which you added product to cart, notification will be shown again when you refresh the page.
If you go to the other page, notification will not be shown. So mean that woocommerce notification works with browser cookie.
So if cookie isn't removed, notification is shown again. This is not bug.
Please don't worry about this problem. This is just related with cookie, not related woocommerce payment or cart logic.
If you have any question, please let us know again without hesitation.
Best Regards, C-Themes