I don't have a short course story, but I guess my long course story is somewhat related.
I had just started running road races as a college student after a high school career as a mid distance guy. I showed up to what was probably my 5th or 6th race, which was on the 5K road loop at Penn State. Anyone who has run in the State College area knows that a good 50% of the races in town are on this loop, so even as a new road racer, I had run the course a few times and I knew the loop.
I had been steadily dropping time over my first few races and I was probably on pace for another PR. Half way through the race, I was running fairly well with the two leaders probably 50 meters ahead and one guy between the leaders and I. After the two mile mark, you are supposed to turn right onto a little side road which takes you up to the road leading into the finish. Well, the leaders apparently didn't know where the turn was, and for some reason the volunteer who was standing at the turn didn't tell them to turn. They cruised right past the turn and continued to the T at the end of the road before turning(adding about a quarter mile to the race).
Seeing this happen in front of me, I had a bit of a decision to make. I knew that I could run the right way and probably win, but that seemed like somewhat of a meaningless victory to me, so I followed the course that the leaders had set.
Apparently the volunteer at the turn realized her mistake shortly after I passed and directed everyone after me to go the right way, so the leaders and I came around the turn on our lengthened course to find that we were now in about 20th place. The guys in front of me, who were much better than me at the time, just went ahead and blew past all of the guys who had popped out in front of us and went on to take first and second despite running an extra quarter. I passed a few, but didn't regain my original place. I didn't PR that race (I guess technically I PRed at the the 5.25K).
Since it was just a friendly road race, they decided to adjust our times. One of the other runners walked over to us after the race and asked the leader what time he would have run in an actual 5K and they took the difference and subtracted it from each of our times to come up with adjusted places.