As a sidenote, it is rather easy to use More Fields instead, to insert a custom field called “CSS” that outputs to the header.
http://wordpress.org/extend/plugins/more-fields/
Just wanted to confirm that I am having the same problem.
I had a trouble with Super Cache too, and i fixed it by removing the plugin, and replace it with a custom field.
http://wordpress.org/support/topic/331803?replies=3
the way that art direction is written, when the_content is called, it takes page output, caches it, replaces the closing HEAD tag with it’s styles and script (and a new closing HEAD tag)
this is probably causing problems with generating cache. it messes with full page output. really should probably use enqueue script or some of the built-in functionality to output content in the header when wp_head is called.
to fix a different problem with art direction i changed the event bound to wp_head – http://wordpress.org/support/topic/330344 not sure that will help with super cache, but it’s worth a try.