If a CSS file is imported that then contains other @import statements, those files will not be imported.
Example (open the demo.php page)
For root URLs, the problem seems to be from the resolveRootedPath() method. If I just return from that method before the final value reassignment, it finds the file, but when it tries to do its move upwards in the directory thing it changes to a missing file.
Made some changes to better handle rooted URLs (issue #50).
Also some refactoring and removal of redundant comments for readability.
Thanks for your bug report and attached code.
I think I've got to the bottom of this and checked in some changes. All seems to work as expected now.