This post contains three bug reports and a UX issue. I reproduce two of the bugs in this video.

1. Bug: The comment box is displayed when I cannot comment. Consider this page: https://community.spotify.com/t5/Closed-Ideas/Playback-Speed/idi-p/993793#comments When logged out, I see a comment box at the bottom. I fill it in, submit it, am prompted to log in, and am told that I don't have permission to post it. When logged in, I do not see a comment box (presumably because I don't have permission, presumably because the topic is closed). Expected behaviour: the comment box should not be displayed to me when I can't comment on it, regardless of whether I'm logged in or out.

2. Bug: Sent to the wrong page after login (possibly worse than this). I'm logged out and I open two topics, each in their own tab. I go to the first topic in the first tab and submit a comment. It prompts me to login before it accepting the submission. After I login, it redirects me to the second topic even though I submitted from the first. Expected behaviour: I'm redirected to the first topic as that is the topic I submitted. Possibly more bugs: I didn't test this because that would require making actual posts, but if the comment submission is associated to the comment through the same mechanism that the return link is generated, then if I had been allowed to comment, it would have placed the comment on the wrong topic. Probable cause: The last page I opened is being stored somehow  based on my session and I'm being redirected to that location. Probable solution:  Grab the Referrer[sic] header off the initial form submission (a quick test implies the browser will set this on the redirect in the way that would be desired for this, though probably check the RFC I linked before depending on that). I show what this header looks like in the demonstration video I linked above. If you do need to store it and pass it around for some reason, then stick it in a query parameter which is scoped to the request, not my session which is scoped to  my cookies and thus interfered with by other requests.

3. Bug: Unable to submit a topic when a different tab logs out and in. Open two tabs. In the first tab, make a new topic and write a post but don't submit it. In the second tab, log out and then log back in. In the first tab, submit the topic. It fails and possibly loses the data (it was available when I hit my browser's back button, I'm not sure if my browser hung onto it or if the autosave pulled it back up). For clarity, that's two posts lost between my original comment and the successful submission of this post. Expected behaviour: It should successfully submit the topic since I was logged in both when I started writing the post and when I submitted the post.

4. UX Issue: The "Post an Idea" link is very difficult to find. I almost gave up and didn't post this. I would advocate asking someone who hasn't used the site to submit a topic requesting some feature. Then step back and watch them. Do not interfere with their effort, even if it feels like this. The purpose is to understand how the user thinks/behaves/interacts, not to correct them, correcting them masks the problem.