I have just done exactly the same request, and I get a proper response
with a proper Content-Length. Also using curl on Gentoo:

$ curl --version
curl 7.12.0 (i686-pc-linux-gnu) libcurl/7.12.0 OpenSSL/0.9.7e zlib/1.2.2
Protocols: ftp gopher telnet dict http file https ftps
Features: Largefile NTLM SSL libz
$ curl -C 3715816 http://homepage.mac.com/dailysourcecode/DSC/DSC-2005-03-15.mp3 >/dev/null
** Resuming transfer from byte position 3715816
... download proceeds to fetch 608k ...
... server appears to stop transferring data after 400-600k ...
curl: (18) transfer closed with 12365102 bytes remaining to read

Request headers:
    GET /dailysourcecode/DSC/DSC-2005-03-15.mp3 HTTP/1.1
    Range: bytes=3715816-
    User-Agent: curl/7.12.0 (i686-pc-linux-gnu) libcurl/7.12.0 OpenSSL/0.9.7e zlib/1.2.2
    Host: homepage.mac.com
    Pragma: no-cache
    Accept: */*

Response headers:
    HTTP/1.1 206 Partial Content
    Accept-Ranges: bytes
    Date: Wed, 16 Mar 2005 14:17:58 GMT
    Content-Length: 12987694
    Content-Type: audio/mpeg
    Server: Apache/1.3.33 (Darwin)
    Last-Modified: Tue, 15 Mar 2005 16:37:46 GMT
    ETag: "212a498-fee016-42370f5a"
    Content-Range: bytes 3715816-16703509/16703510
    x-responding-server: web
    Via: 1.1 netcache02 (NetCache NetApp/5.5R4)

Headers looks fine. The download does stop after tranferring 400-600k
though - it appears as though the server simply stops sending data
after a while.

Compare with:

> bash-2.05b$ curl --version
> curl 7.12.0 (i686-pc-linux-gnu) libcurl/7.12.0 OpenSSL/0.9.7e ipv6
> zlib/1.2.2
> Protocols: ftp gopher telnet dict http file https ftps
> Features: IPv6 Largefile NTLM SSL libz
>
> I've also tried it on a Mandrake 8.2 box...
> daniel_at_gateway daniel]$ curl --version
> curl 7.9.4 (i586-mandrake-linux-gnu) libcurl 7.9.4 (OpenSSL 0.9.6i)
>
> The headers..
> HTTP/1.1 206 Partial Content
> Accept-Ranges: bytes
> Date: Wed, 16 Mar 2005 12:07:06 GMT
> Content-Length: 0
> Content-Type: audio/mpeg
> Server: Apache/1.3.33 (Darwin)
> Last-Modified: Tue, 15 Mar 2005 16:37:46 GMT
> ETag: "212a498-fee016-42370f5a"
> Content-Range: bytes 3715816-16703509/16703510
> x-responding-server: web
> Via: 1.1 netcache02 (NetCache NetApp/5.5R4)

-- Jamie
Received on 2005-03-16