The answer: https://security.stackexchange.com/a/23431/10863
The timeline as I understand it:
- The question is about Nmap and one of the original authors of Nmap answers.
- They copy the answer to their wiki two weeks later.
- Some time later, a moderator later sees that the answer is identical to the website and deletes for blatant plagiarism.
- The author edits, explaining that it's perfectly within his rights to post it in both places, both under the CC-BY-SA license and because he holds the copyright; moreover, the Sec.SE answer was first. It's clearly not plagiarism.
- The author adds a link from their wiki to Sec.SE, saying "This page originally appeared as an answer on [Sec.SE]", linking the answer.
- Radio silence. I guess the moderator did not see it.
- I found the answer on their wiki, see what happened, and try to undelete. I get the message "A moderator has deleted this post and cannot be undeleted."
Apparently moderators are considered infallible by SE, but that issue has an (old) open feature request on meta.SE so I won't open another topic for that. I do think the site's behaviour is rather weird here, we might want to be hesitant to use mod powers for deletion.
I see no reason for this answer to be deleted. I can see where the confusion came from and it's definitely not malicious on the moderator's part, I'm not complaining about the moderation, but the author clarified the situation and it looks to me like it should have been undeleted pronto.
I'm not sure what to tag it with, since it's not a discussion, I do not need support using the site (it has been made impossible for me to use the site as designed: despite having undelete voting powers, I cannot vote to undelete), and while the behaviour might be considered a bug or feature request, that is not the goal of this question. This question aims to seek moderator support and warn/inform others about the issue with the website. I'll tag with discussion because maybe someone else has thoughts on the matter.
Edit: I just saw that the top voted answer is another answer by OP. The link from their wiki seems to be outdated (it links the deleted answer).