HTTP Upload through proxy

Not sure if this is the right list or not because i'm actually
experiencing this using 1.3. =20

We have a form behind a mod_proxy based reverse proxy.  That form
functions correctly if accessed directly, however when i access it
through the proxy, the body of the upload file doesn't get sent back to
the backend server.  The backend server then replies with a 100 Continue
to which the proxy doesn't react.  The browser hangs while the proxy
sits around, till mod_proxy eventually kills it's connection to the
backend server and returns a 502 Bad Gateway to the client.

I haven't been able to find anything on the web related to this, which
makes me think it's something goofy about our configuration (apache is
compiled with mod_perl, mod_proxy and mod_rewrite, statically).  Any
ideas on where i can look to try to fix this would be appreciated.

Adam