I encountered this question today:
Which had the exact same title as this question, and even called out that it was essentially a duplicate of it.
I went to try to close and gently advise the asker that creating a duplicate question just because another question is unanswered is probably not the right approach.
Only problem is when searching for the duplicate, nothing comes up. My guess is the text search pares out an exact match (assuming it is the question, and that no one would ever use the exact same title, as most duplicates are an accident).
I don't really have any more time to fix this. I tried changing the title of each question in hopes it would allow me to successfully search the original question to flag the dupe. My guess is there is some search index caching going on or something. But maybe someone else will have better luck or can say what to do to fix these.
Can moderators bring down the hammer all by themselves and summarily close a question?
I would class this as a bug, as well. Clearly flagging a dupe, that is dupe should be possible when the original is an exact match of title.
Or maybe an exact title match should automatically flag the moderator? It's an edge case, I grant, but this can't be the first time this has annoyed someone in a stack exchange or SO.