The question https://softwarerecs.stackexchange.com/posts/4539/revisions was closed as a duplicate of https://softwarerecs.stackexchange.com/posts/4529/revisions. Given that the second question was at the time merged into the first one, this effectively made the question closed as a duplicate of itself.
This is a bug: questions should be prevented from self-duplicate closure, even when merged.
Related: http://meta.stackexchange.com/questions/286745/reopen-post-when-its-duplicate-is-merged-into-it when things happen in the opposite order (close then merge).
Merging should be restricted to questions where one has already been marked as a duplicate as the other. This would avoid the self-duplicate bug since duplicate loops are already prevented. It would also be a UX improvement: merging is a dangerous tool and the merging UI is pretty bare compared with the duplicate UI (in particular, the merging UI doesn't display the proposed duplicate like the exact duplicate does). It would mean one more step when moderators merge questions, but only when they aren't already duplicates, and merging is rare anyway.
