Indeed, that became a habit for me a while ago after certain social discussion sites and on-line tools I use frequently went all Web 2.0 and broke the back button when a form submission failed, typically because the form fields were only added dynamically using JS so when you go back they simple aren't there any more according to your browser. Mercifully, HN has yet to introduce that particular "improvement".
That's not really the point, though, is it? The important thing is whether posters who want to offer a useful comment and/or mitigate a poor comment can do so. Once HN gets into unknown/expired mode at the moment, it seems common that even basic things like "More" links and logging in can fail as soon as you load/refresh a page, at which point the site is effectively unusable: you can't contribute even if you have something worthwhile to add saved away in your clipboard from the previous failed attempt.
Firefox: https://addons.mozilla.org/en-US/firefox/addon/lazarus-form-...
Chrome: https://chrome.google.com/webstore/detail/loljledaigphbcpfhf...