LWP will return a 500 status code when it can't connect to the server. From a web server, it indicates a problem on the server, usually a CGI script dying. With LWP, it can indicate a network connection problem. In this case, this is what is happening.

I would suggest that this is a bug in LWP::UserAgent. It should instead choose another code, or not return a code at all. This behavior can be turned with the use_eval option.