Hi,
In fact, one error should be shown but depending your HikaShop configuration, it is possible to have some cases when it does not work properly.
Because you are using the "add to cart popup", that popup is always display to the customer ; even if the product is not added to the cart.
That is an issue in the HikaShop cart system that I have fixed with the refactoring in HikaShop 3.
HikaMarket uses an HikaShop trigger to authorize or refuse the addition of the product in the cart ( onAfterProductQuantityCheck ) ; that trigger is in the cart class for the function which verify the limits (min/max per order, product limits, etc).
Thanks to that trigger, HikaMarket can change the product quantity but, HikaShop will still consider that the product has been added to the cart for the "popup" part. Some Joomla message will be added saying that the "limitation has been reached".
You will have the exact same displaying issue if you set a limitation on the product and you reach it.
That's why for the refactoring in HikaShop 3 ; I rewrote the entire structure of the cart system in order to allow new features and change how the "add to cart popup" is made.
Regards,