I've seen this repeatedly with Firefox, probably because I always throw out all browser
cookies on exit; the refresh trick always fixes it.
This is how the problem occurs for me:
1. I'm not logged in and click on an article that requires subscription; LWN informs me that I
can't see this article.
2. I click on "log in to read this article"; https://lwn.net/login?target=/Articles/268783/
3. After filling in username and password, I'm redirected to the
http://lwn.net/Articles/268783/ page without the "reply to this comment" buttons -- as if LWN
thought I wasn't logged in.
4. Reloading the page makes the buttons appear.
To reproduce the bug again, I have to clear my cache (!) after logging out. This would suggest
login, but gets cached pre-login by the browser. However I couldn't find such dependencies on
the LWN site.