however I have made a little progress insofar as understanding the issue. not so much for how to fix it.

i used ig's suggestion on wireshark to watch the packet transfers. First thing I noticed is that the browser is doing a CONNECT request, not a POST. When I switched to a CONNECT method in the script I immediately got a 200 return code. Still no content though.

after re-checking the packet capture I saw that after the initial CONNECT and 200, the browser and server do a short handshake dance followed by several application data packets coming from the server to the browser. The LWP request doesn't capture any of that since (I guess) they aren't direct responses to the original request.

Just in case you were curious...