I am not able to recreate your particular issue locally but my guess is that your server is throwing a fatal error which is why it’s outputting nothing to the browser. If you can, turn error reporting on or check your error logs and you tell me what errors you are receiving so I can better help fix your exact issue. My guess is that it’s something particular to your setup. What other plugins do you have activated and what theme are you using?
If I do this on a fresh install of WP 3.5.1 I do not get errors but the plugin does continue to combine CSS files which is definitely a bug. However, I cannot get it to fail like you have on your site.
I have patched this for now but I am going to hold off on rushing a release out to ensure I don’t break anyone else using this plugin. If you can let me know the exact errors you’re receiving that would be great and thank you for your detailed initial question.