hmm, that's interesting because i don't see any conflict problem on your website. There is no logical reason why the quantityPlus button doesn't work. Because increasing the quantity upon clicking the PLUS icon is handled by this JS file:
/components/com_virtuemart/assets/js/vmprices.js
Actually through this function:
plus.click(function() {
var Qtt = parseInt(quantity.val());
if (!isNaN(Qtt)) {
quantity.val(Qtt + Ste);
Virtuemart.setproducttype(cart,virtuemart_product_id);
}
});
have you ever touched this vmprices.js file? Also, try to temporarily unpublished the Ajax dock cart module and see if it helps.
Regards,
Support