Hi,
Well, it's more than up until now the information you provided to reproduce the problem was not precise enough and we didn't had the problem on our end in the various tests we made.
I was actually able to reproduce the issue today and apparently, this only happens in carts where you have products where you directly assign the quantity to the variants themselves. If the product has no variant or that the quantity is set at the product level this issue doesn't happen.
So thank you for your feedback, it's alwasy great to fix issues, even small ones like this one, but it would be great if you could provide more precise information next time when you report one. That will reduce the back and forth between us and it will make everyone happier 
So I've made a patch on our end by changing the code:
if($this->row->product_quantity > 0)
$max_quantity = min($max_quantity, $this->row->product_quantity);
to:
if($this->row->product_quantity > 0) {
if($max_quantity == 0)
$max_quantity = $this->row->product_quantity;
else
$max_quantity = min($max_quantity, $this->row->product_quantity);
}
in the file components/com_hikashop/views/layouts/tmpl/quantity.php
It now works fine on my tests with that patch (note that if you have an override of layouts/quantity.php you need to do that change in the view override.