Issue with adding library/framework CSS files in blueprint_preprocess()

So I _THINK_ there might be an issue with drupal_css_add() calls for the 'blueprint/screen.css' and 'blueprint/print.css' framework stylesheets located in the libraries directory. I don't fully understand where the breakdown is, but I found that some "pages" don't end up having those two stylesheets when the page is rendered. Two examples are Ubercart's shopping /cart page and even the /user/login "page".

I solved the issue by putting the following into my subtheme_preprocess_page()

$vars['css'] = drupal_add_css();
$vars['css_alt'] = blueprint_css_reorder($vars['css']);
$vars['styles'] = drupal_get_css($vars['css_alt']);

This seems to rebuild the $styles variable in time for page rendering on normal pages (with nodes in them) and for special "pages" like /user/login and /cart.

I'm don't seem to fully understand the issue, so hopefully my explanation and solution makes sense.

..jon