.info styles load before base theme
I would be curious to hear a alternative solution but this works too (albeit hackish):

I removed the reference to the stylesheet in *.info and simply added the call inside template.php:

function MYTHEME_preprocess_html(&amp;$vars) {
    drupal_add_css(path_to_theme().'/styles.css', array(
      'group' =&gt; CSS_THEME, 
      'preprocess' =&gt; FALSE
    ));
}