I can confirm that this is an issue with the way WordPress is serving file. On my Powerpress-powered WP blog, the podcast fails the byte-range requests check if the podcast contains WP URLs — specifically, those generated by uploading to WordPress under “Add Media”. However, it passes when the URLs are non-WP, like if I upload the files to a subdirectory of my site via FTP. This is the same exact server: works with non-WP links, fails with WP links. The only explanation I can think of is that somehow WP is serving the files uses a backend PHP script which bypasses the server config and fails to allow byte-range requests. Perhaps this should be filed as a bug and/or feature request?
