Maybe, but I can't imagine they would be very upset by the interviewer continuing to take a little more of their time either. At the very least, it gives you the feeling that the interviewer fairly assessed you instead of dismissing you because of one flummoxed question. When I interview someone who quickly seems unlikely to pass an intervew, I try to use as much time as possible to make sure my initial impression was correct and the candidate just didn't get unlucky and/or just happens to be overly nervous. Some people are great employees but are bad at being interviewed.