Did the application generate the link that you are having trouble with?
Glancing at discourse/config/routes.rb at main · discourse/discourse · GitHub it doesn’t look like it’s a valid route.
If you start on a route that is invalid, rails isn’t going to send you the entire ember application to tell you that you have a bad URL.
Looks like I’m wrong, https://meta.discourse.org/bananas loads the oops page. I guess it’s because /posts/:id/xxx is a valid route.