Isn't that a potential information leak, though? A potential black-hat attacker could sit around and brainstorm a big list of potential vulnerabilities without going through to figure out if they exist and are exploitable. Then they can start submitting them, and if they get closed as duplicate, they can quickly dive into that one, figure out how to exploit it, and make use of it for nefarious purposes.

Maybe that's a little farfetched, though.