I noticed a question that was closed as duplicate, but the dupe targets were wrong. Gold hammer edited the list to add another target in addition to the original, but still both were wrong.
I did find a correct dupe target, so I reopened the question (using my own hammer) and closed as duplicate of the other question I found. To my surprise, the wrong duplicates appeared again!
I had to manually edit the list of duplicates, and now it's fine. Still, reopening should clear this list.
The bug can be seen in the revisions list: