I just successfully added my Close vote to a question on Stack Overflow that had already been deleted by the author. The question can be found here.
The only purpose I see for such functionality is perhaps to stop someone from escaping the initial surge of wrath from critics, then subsequently undeleting their question. And that would be a pretty strange thing to guard against. It seems far more likely that this is an oddity that was overlooked.
So I'm just curious - is voting to close a deleted question a bug, or is it status-bydesign? If by design, what is the rationale behind it?