Currently, this behaves correctly if you start a reply using the quote button, but the issue still occurs if you have an existing reply and use the quote button to add text to it. If the quote contains a link, and the other conditions for the warning are met (quoted post sent within the last two weeks), you’ll see the duplicate-link warning.
Quoting the warning message so someone searching for it can find this thread:
It looks like your link to [domain] was already posted in the topic by [user] in a reply on [date] – are you sure you want to post it again?
Hmm, okay. I’m probably misunderstanding the purpose of the warning. My assumption was that it was basically a heuristic to detect redundant discussion: if your post happens to include the same link as another post, you probably didn’t read that post (or else you wouldn’t have thought it necessary to post the link again), and you’re probably trying to make a similar statement (since both you and the other poster thought the link was relevant). That reasoning wouldn’t apply if you’re quoting the other post to respond to it.
If the warning appearing in this case is correct, then the bug is that it doesn’t appear if you use the quote button to start a reply. For some reason it seems to hit the postNumber === linkInfo.post_number check in link-lookup.js.es6.
