Because HttpProxy renames form input elements by prepending "HttpProxy_", javascript tied to those elements fail. This is a real issue with proxied content created with GUI builders (VS.NET, StudioCreator) where tweaking the scripts is a pain. As a quick hack, stripping out the "HttpProxy_" from HttpProxy and HttpProxy::Parse works, but it would be nice if this was configurable. for examples of the "stripped" code, see: http://www.plainblack.com/etcetera/httpproxy-form-variable-re-writing/1