I setup a Drupal site on two domains (www.example.com and blog.example.com); I am using the Domain module.
I also setup a fake cdn.example.com domain on the same DOCUMENT_ROOT folder; I am using the CDN module for this.
I setup boost for static page cache with aggregation and minimalization of CSS and JavaScript files.
At first, everything was right and the files were served correctly from cdn.example.com. After some time (I don't know how long), something changed. The boost cache files referring to the CSS and JavaScript files are served not via http://cdn.example.com, but https:/blog.example.org (note the https instead of http). Since my blog.example.org does not have a SSL certificate, the files won't get requested and my style is broken.
When I flush the cache, everything works again.
I updated the modules and Drupal core to the latest stable production versions.
Why do I have this behavior?