How to fix your template to add css-class-suffix
You are probably using a 3rd party template which uses a module-override which is not parsing the module css-class-suffix properly. Templates by YOOtheme and some Artiseer templates seem to have this issue.
In case you want to hide modules with Frontend-User-Access and are wondering if this is a template issue, set your site-template to Joomla's default 'rhuk_milkyway' and check if modules are hidden.
What some templates do wrong is that they totally ignore the css-class-suffix as set in the module configuration (try it!). To make Frontend-User-Access hide modules, this must be fixed in your template.
The fixes underneath will basically add the suffix to the style, which allows fua to hide it, and giving frontend-developers control over style.
If you have this issue but can not work this out, please contact us. We will be happy to fix your module-override.
Artiseer
file: /templates/template_name/html/modules.php
try find this line:

change to:

If the above code is not in there, try to find this code:
function modChrome_artblock($module, &$params, &$attribs)
{
if (!empty ($module->content))
echo artxBlock(($module->showtitle != 0) ? $module->title : '', $module->content);
}
replace by:
function modChrome_artblock($module, &$params, &$attribs)
{
if (!empty ($module->content))
$sfx = '';
$sfx = $params->get('moduleclass_sfx');
echo artxBlock(($module->showtitle != 0) ? $module->title : '', $module->content, $sfx);
}
AND
file: /templates/template_name/functions.php
find this code:
function artxBlock($caption, $content)
replace by:
function artxBlock($caption, $content, $sfx)
AND
(in the same file a few lines under that)

replace by:

YooTheme
Here is how to fix that in Yootheme's yoo_explorer template:templates\yoo_explorer\html\modules.php
line: 156
$file = dirname(dirname(__FILE__))."/lib/modules/{$template}.php";
replace with:
if($template!='default'){
$style = $style.$suffix;
}
$file = dirname(dirname(__FILE__))."/lib/modules/{$template}.php";