Summary: A broken duplicate list "edit" link is shown to the author of a post in the "possible duplicate" banner when the author also has a gold tag badge and the question is flagged but not yet closed.
Detail: On this question:
- I am the author.
- Somebody flagged it as a duplicate.
It is not closed (and has no CVs, it was only a flag) but the visible-to-OP-only "possible duplicate" notification is displayed:
I have a gold badge in the tag and can thus edit the duplicate list.
And so, the duplicate list "edit" link is displayed. However, since the question is not actually closed, it leads to a 404.
The bug is that the "edit" link should not be displayed unless the question is actually closed. Only the original author of the question would see this (and only if they have a gold tag badge), since this banner isn't publicly visible until the question is actually closed.