Module Class Suffix doesnt work

That's interesting.

It actually works on our dev website but doesn't on our demo website. We will have to investigate...
It's actually a parameter which is handled automatically by joomla and since it was working on our dev website, we thought it would be working all the time.
I'll update that thread when we find the problem.

You can edit the file modules/mod_hikashop/mod_hikashop.php and the file modules/mod_hikashop_cart/mod_hikashop_cart.php and change in each the code

foreach($module_options as $key => $option){
	$params->set($key,$option);
}

foreach($module_options as $key => $option){
	if($key !='moduleclass_sfx'){
		$params->set($key,$option);
	}
}

If you use a space, that means that the module div will have two classes:
module new_class
But if you user an _, it will only have one class which is different from the default one:
module_new_class

Ususally, I used that option to set the suffix _menu which is defined for the menu module in order to add a chrome around the module when displayed on the left or right columns of the template. That's a standard way of doing it in joomla.