Why do FTP specific features over HTTP proxy fail?
Because when you use a HTTP proxy, the protocol spoken on the network will be HTTP, even if you specify a FTP URL. This effectively means that you normally can’t use FTP specific features such as FTP upload and FTP quote etc. There is one exception to this rule, and that is if you can “tunnel through” the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) and is generally not available as proxy admins usually disable tunneling to other ports than 443 (which is used for HTTPS access through proxies).
