In the File > Export > Export Raw Files code, there's a "Skip non-HTTP/200 responses" option. This option is designed for dumping files (either media files or files to be replayed by the AutoResponder) to a folder.
For various reasons, clients and servers often will use Range requests for media downloads, meaning that the response code for a response might be HTTP/206 instead of HTTP/200, even if the full body is present.
To enhance the file exporter, the code should look at the Content-Range response header for a HTTP/206 response. If the header is of the format:
Content-Range: bytes 0-N/N+1
Then Fiddler should treat the response as a HTTP/200 and save the body to disk.