Slightly OT: is that what a 'Discourse' page looks like? It's pretty awful: it will automatically update the URL as you scroll past each post in any direction, while breaking the Back button, so good luck getting back to the original post, since neither clicking on Back nor reloading the page will get you there. Basic UX failure.
It looks like a feature to me : this way when you copy the address it links directly to the right comment. Of course this comes at the expense of a working back button.
The page is using Location.replace[0] to update the URL and replaces the current history entry without affecting back/forward behavior on pretty much any browser.
The one downside is that the URL may no longer point to the comment you were originally linked to.