I had the same thing happen to me about a year ago. I was leading a small 5 miler with four other guys in a chase pack about 20-30 seconds back and I got to a poorly marked corner with a race official lackadaisically sitting on the curb, she didn't notice me until I shouted at her and then she quickly pointed left which is where I went and was subsequently followed by the chase pack. Sure enough the way she pointed brought us to the finish, but when I got there I had a finishing time of 24:xx which I was in no way capable of the at the time (more like 26:xx) and I knew I had run the wrong way at the intersection. I told the RD of the mistake and he then DQ's both myself and the chase pack of four other guys... It sucked but we also didn't run the full distance. The RD was nice enough to give me the gift certificate for 1st place but I obviously wasn't the official winner in the standings.