I just noticed that navigating directly to a user’s page (http://meta.discourse.org/users/gdpelican) breaks the back button functionality (it creates a loop between /users/<username> and /users/<username>/activity)
Seems to work ok when navigating through, say, the user card though.
I believe this is a bug in the Ember framework. I created a workaround previously that rewrites URLs but I couldn’t get the typing or copying and pasting one to work. Fortunately, I think it’s quite a rare case to paste a URL like that then hit back.
I’m hoping the next Ember upgrade fixes it. There are many fixes included and it worked before we upgraded to this release.