I once had an interviewer ask me an obscure C++ question. I didn't know the answer, so I reversed it and asked if he knew. He did, and it taught me something I didn't know before. No, I didn't get the job. I no longer even remember the interviewer's name, but I remember well the question and answer.
When I started doing interviews I also had some C++ questions (like what is the difference between const and define and some random stuff like that), that I was always unsure about: are these things actually telling me that the person is a good C++ programmer, or am I just asking some random stuff that I happen to know?
