I was wondering if it's intentional that at WP's admin side, W3TC does not rewrite the image URL's to point to CDN (AWS S3). Files get properly uploaded and at the public site they images show up properly (with rewritten URL's pointing to CDN).
We're using WP multisite in a load balanced environment. As a result, if an admin page request hits a server that does not have a local copy of the file, the image seems to be broken in the editor. URLs are pointed to http://www.example.com/files/2012/10/image.png that in turn gets rewritten to to /wp-includes/ms-files.php?file=...
In general I do not care even the URL's would stay as they are, but in case that there is no local copy of the file, it would be good that it would be downloaded from the CDN to the server in question.