File: /lib/classes/class.moduleoprations.inc.php 
Function: LoadModules() 
Line: 802 

there it says:

if( isset($CMS_STYLESHEET) && !isset($CMS_STYLESHEET) ) continue;

obviously this weird condition will never be true ;-)
Not sure what you're trying to check here.

It seems to be related to the /admin/style.php (since there $CMS_STYLESHEET is
declared the first time) or to stylesheets at all since in
/plugins/cms_stylesheet.php the $CMS_STYLESHEET variable is temporarily set to 1
and after stylesheet processing back to 0 (and even unset afterwards) to tell
the core that you're not on css processing anymore.

From my understanding you try to avoid loading modules if stylesheets are
processed (for whatever reason), don't you?

However either this condition is obsolete or it should be changed to whatever
you try to achieve here.

Kind regards.