I would say this is actually a very important part of interviewing. When given vague requirements, see how they respond. Building something that is technically correct isn't as good as building what you actually want.
I'd give the candidate some minutes to Google the problem, but then I'd want a solution and a good explanation. (Explaining other people's code is hard, too.)
Thanks autokad. base698 has the right interpretation: My response was the smarmy answer I have given in interview situations where I just felt rebellious against the energy of interviewer combined with the test questions. I actually agree with base698. An understanding of the basics is required. And the companies I've coded for - for long periods of time, and loved working at - figured out I knew the basics based on our conversations alone. I hire people without testing. It has not backfired yet. I have also tested others in the past, had people pass the test, only come on board to be dangerous to production environments.
In elementary school when you were learning to do algebra did you say, "that problem has been solved id google it?" To learn you have to do the basics before you can do the advanced stuff.
poorly specified questions are very important to ask IMHO :)