While trying to find a way to redirect to a "server relative URI" I found that the documentation had listed URLRedirectForwardAction as Deprecated. The alternative is/was to use 'Http302ForwardAction'. Unfortunately Http302ForwardAction appends the server reference to the redirect. In our case it would append "http://localhost:1776" to the front of "/new-page" which obviously won't work when sending it to the browser.
I opened a ticket.
According to HP support the documentation stating that URLRedirectForwardAction has been deprecated is not correct and it will not be retired soon.
Too late for me - I had already extended Http302ForwardAction to not append the server.