Thank you for the bug report. That's actually a problem only when you use normal button styling in the config under the tab display. With CSS styling on buttons, it works like you say it should (which is why we didn't see the problem).
You can edit the file quantity of the view product and change the line:
echo $this->cart->displayButton(JText::_('CHOOSE_OPTIONS'),'choose_options',$this->params,hikashop::completeLink('product&task=show&product_id='.$this->row->product_id.$this->itemid),'','');
to:
echo $this->cart->displayButton(JText::_('CHOOSE_OPTIONS'),'choose_options',$this->params,hikashop::completeLink('product&task=show&product_id='.$this->row->product_id.$this->itemid),'window.location = \''.hikashop::completeLink('product&task=show&product_id='.$this->row->product_id.$this->itemid).'\';return false;','');