I don't think the patch in pull request 6338 is right. I experienced the issue defined in WLFY-3448 on 8.1.0.Final, then built master at 50a830205c and the new behavior is different but still broken. Now requests to http://host/login throws a Not Found, the server is expecting http://host//login (which explodes because it isn't valid). If I hit http://host then the redirect is generated to http://host//welcome because httpServletRequest.getContextPath() is returning "/" (when it was returning an empty string in 7.x).
My app is packaged as a war, so no application.xml exists to define context-root.
I would say this is a regression caused by the resolution to WLFY-3448