Please remove your modification for the add to cart button over the text issue. That was indeed not the good way to do it. I was a bit too fast and didn't read what was the text above the button ( without syaing that it was in swedish which didn't help me to notice ). The fact that the button is now in double is because you didn't do the correct modification.
Instead of the previous modification, edit the file components/com_hikashop/views/product/tmpl/quantity.php near line 35 and change the code
echo JText::sprintf('X_ITEMS_IN_STOCK',$this->row->product_quantity);
echo '<br/>';
to
echo JText::sprintf('X_ITEMS_IN_STOCK',$this->row->product_quantity);
echo '<br/>';
$config =& hikashop::config();
if($config->get('button_style','normal')=='css'){
echo '<br />';
}