Hi,
That's because, on a products listing, even if you have turned off the display of the custom item fields, HikaShop needs to load the custom item fields from the database to know if it can display the add to cart button or the "choose options" button.
And when the custom item fields are loaded, the javascript for the "display limited to" setting will be added to the page.
Change the line:
if(!empty($productClass->itemFields)) {
to:
if(!empty($productClass->itemFields) && $this->params->get('display_custom_item_fields', 0)) {
in the file components/com_hikashop/views/product/view.html.php and that will avoid loading the javascript of the custom item fields when they are not to be displayed on the listings.
Please let us know how it works so that we can add that improvements in the next release of HikaShop.